The OAuth 2.1 Authorization FrameworkSignIn.Orgdick.hardt@gmail.comOktaaaron@parecki.comhttps://aaronparecki.comyes.comtorsten@lodderstedt.net
Security
OAuth Working GroupInternet-DraftThe OAuth 2.1 authorization framework enables a third-party
application to obtain limited access to an HTTP service, either on
behalf of a resource owner by orchestrating an approval interaction
between the resource owner and an authorization service, or by allowing the
third-party application to obtain access on its own behalf. This
specification replaces and obsoletes the OAuth 2.0 Authorization
Framework described in RFC 6749.IntroductionIn the traditional client-server authentication model, the client
requests an access-restricted resource (protected resource) on the
server by authenticating with the server using the resource owner's
credentials. In order to provide third-party applications access to
restricted resources, the resource owner shares its credentials with
the third party. This creates several problems and limitations:
Third-party applications are required to store the resource
owner's credentials for future use, typically a password in
clear-text.
Servers are required to support password authentication, despite
the security weaknesses inherent in passwords.
Third-party applications gain overly broad access to the resource
owner's protected resources, leaving resource owners without any
ability to restrict duration or access to a limited subset of
resources.
Resource owners often reuse passwords with other unrelated
services, despite best security practices. This password reuse means
a vulnerability or exposure in one service may have security
implications in completely unrelated services.
Resource owners cannot revoke access to an individual third party
without revoking access to all third parties, and must do so by
changing the third party's password.
Compromise of any third-party application results in compromise of
the end-user's password and all of the data protected by that
password.
OAuth addresses these issues by introducing an authorization layer
and separating the role of the client from that of the resource
owner. In OAuth, the client requests access to resources controlled
by the resource owner and hosted by the resource server.
Instead of using the resource owner's credentials to access protected
resources, the client obtains an access token - a credential representing
a specific set of access attributes such as scope and lifetime. Access
tokens are issued to clients by an authorization server with the approval
of the resource owner. The client uses the access token to access the
protected resources hosted by the resource server.For example, an end-user (resource owner) can grant a printing
service (client) access to their protected photos stored at a photo-
sharing service (resource server), without sharing their username and
password with the printing service. Instead, they authenticates
directly with a server trusted by the photo-sharing service
(authorization server), which issues the printing service delegation-
specific credentials (access token).This specification is designed for use with HTTP (). The
use of OAuth over any protocol other than HTTP is out of scope.Since the publication of the OAuth 2.0 Authorization Framework ()
in October 2012, it has been updated by OAuth 2.0 for Native Apps (),
OAuth Security Best Current Practice (),
and OAuth 2.0 for Browser-Based Apps ().
The OAuth 2.0 Authorization Framework: Bearer Token Usage ()
has also been updated with (). This
Standards Track specification consolidates the information in all of these
documents and removes features that have been found to be insecure
in .RolesOAuth defines four roles:
"resource owner":
An entity capable of granting access to a protected resource.
When the resource owner is a person, it is referred to as an
end-user. This is sometimes abbreviated as "RO".
"resource server":
The server hosting the protected resources, capable of accepting
and responding to protected resource requests using access tokens.
The resource server is often accessible via an API.
This is sometimes abbreviated as "RS".
"client":
An application making protected resource requests on behalf of the
resource owner and with its authorization. The term "client" does
not imply any particular implementation characteristics (e.g.,
whether the application executes on a server, a desktop, or other
devices).
"authorization server":
The server issuing access tokens to the client after successfully
authenticating the resource owner and obtaining authorization.
This is sometimes abbreviated as "AS".
The interaction between the authorization server and resource server
is beyond the scope of this specification, however several extension have
been defined to provide an option for interoperability between resource
servers and authorization servers. The authorization server
may be the same server as the resource server or a separate entity.
A single authorization server may issue access tokens accepted by
multiple resource servers.Protocol FlowAbstract Protocol Flow| Resource |
| | | Owner |
| |<-(2)-- Authorization Grant ---| |
| | +---------------+
| |
| | +---------------+
| |--(3)-- Authorization Grant -->| Authorization |
| Client | | Server |
| |<-(4)----- Access Token -------| |
| | +---------------+
| |
| | +---------------+
| |--(5)----- Access Token ------>| Resource |
| | | Server |
| |<-(6)--- Protected Resource ---| |
+--------+ +---------------+
]]>The abstract OAuth 2.1 flow illustrated in describes the
interaction between the four roles and includes the following steps:
The client requests authorization from the resource owner. The
authorization request can be made directly to the resource owner
(as shown), or preferably indirectly via the authorization
server as an intermediary.
The client receives an authorization grant, which is a
credential representing the resource owner's authorization,
expressed using one of two authorization grant types defined in this
specification or using an extension grant type. The
authorization grant type depends on the method used by the
client to request authorization and the types supported by the
authorization server.
The client requests an access token by authenticating with the
authorization server and presenting the authorization grant.
The authorization server authenticates the client and validates
the authorization grant, and if valid, issues an access token.
The client requests the protected resource from the resource
server and authenticates by presenting the access token.
The resource server validates the access token, and if valid,
serves the request.
The preferred method for the client to obtain an authorization grant
from the resource owner (depicted in steps (1) and (2)) is to use the
authorization server as an intermediary, which is illustrated in
in .Authorization GrantAn authorization grant is a credential representing the resource
owner's authorization (to access its protected resources) used by the
client to obtain an access token. This specification defines two
grant types - authorization code
and client credentials - as well as an extensibility
mechanism for defining additional types.Authorization CodeAn authorization code is a temporary credential used to obtain an access token.
Instead of the client
requesting authorization directly from the resource owner, the client
directs the resource owner to an authorization server (via its
user-agent as defined in ), which in turn directs the
resource owner back to the client with the authorization code.
The client can then exchange the authorization code for an access token.Before directing the resource owner back to the client with the
authorization code, the authorization server authenticates the
resource owner, and may request the resource owner's consent or otherwise
inform them of the client's request. Because the resource owner
only authenticates with the authorization server, the resource
owner's credentials are never shared with the client, and the client
does not need to have knowledge of any additional authentication steps
such as multi-factor authentication or delegated accounts.The authorization code provides a few important security benefits,
such as the ability to authenticate the client, as well as the
transmission of the access token directly to the client without
passing it through the resource owner's user-agent and potentially
exposing it to others, including the resource owner.Client CredentialsThe client credentials or other forms of client authentication
(e.g. a client_secret or a private key used to sign a JWT)
can be used as an authorization grant when the authorization scope is
limited to the protected resources under the control of the client,
or to protected resources previously arranged with the authorization
server. Client credentials are used as an authorization grant
typically when the client is acting on its own behalf (the client is
also the resource owner) or is requesting access to protected
resources based on an authorization previously arranged with the
authorization server.Access TokenAccess tokens are credentials used to access protected resources. An
access token is a string representing an authorization issued to the
client. The string is considered opaque to the client, even if it has
a structure. Depending on the authorization server, the access token
string may be parseable by the resource server.Access tokens represent specific scopes and durations of access, granted by the
resource owner, and enforced by the resource server and authorization server.The token may be used by the RS to retrieve the authorization information,
or the token may self-contain the authorization information in a verifiable
manner (i.e., a token string consisting of a signed data payload). One example
of a token retrieval mechanism is Token Introspection , in which the
RS calls an endpoint on the AS to validate the token presented by the client.
One example of a structured token format is ,
a method of encoding access token data as a JSON Web Token .Additional authentication credentials, which are beyond
the scope of this specification, may be required in order for the
client to use an access token. This is typically referred to as a sender-constrained
access token, such as Mutual TLS Access Tokens .The access token provides an abstraction layer, replacing different
authorization constructs (e.g., username and password) with a single
token understood by the resource server. This abstraction enables
issuing access tokens more restrictive than the authorization grant
used to obtain them, as well as removing the resource server's need
to understand a wide range of authentication methods.Access tokens can have different formats, structures, and methods of
utilization (e.g., cryptographic properties) based on the resource
server security requirements. Access token attributes and the
methods used to access protected resources may be extended beyond
what is described in this specification.Refresh TokenRefresh tokens are credentials used to obtain access tokens. Refresh
tokens are issued to the client by the authorization server and are
used to obtain a new access token when the current access token
becomes invalid or expires, or to obtain additional access tokens
with identical or narrower scope (access tokens may have a shorter
lifetime and fewer permissions than authorized by the resource
owner). Issuing a refresh token is optional at the discretion of the
authorization server, and may be issued based on properties of the client,
properties of the request, policies within the authorization server, or
any other criteria. If the authorization server issues a refresh
token, it is included when issuing an access token (i.e., step (2) in
).A refresh token is a string representing the authorization granted to
the client by the resource owner. The string is considered opaque to
the client. The refresh token may be an identifier used to retrieve the
authorization information or may encode this information into the
string itself. Unlike access tokens, refresh tokens are
intended for use only with authorization servers and are never sent
to resource servers.Refreshing an Expired Access Token| |
| | | |
| |<-(2)----------- Access Token -------------| |
| | & Refresh Token | |
| | | |
| | +----------+ | |
| |--(3)---- Access Token ---->| | | |
| | | | | |
| |<-(4)- Protected Resource --| Resource | | Authorization |
| Client | | Server | | Server |
| |--(5)---- Access Token ---->| | | |
| | | | | |
| |<-(6)- Invalid Token Error -| | | |
| | +----------+ | |
| | | |
| |--(7)----------- Refresh Token ----------->| |
| | | |
| |<-(8)----------- Access Token -------------| |
+--------+ & Optional Refresh Token +---------------+
]]>The flow illustrated in includes the following steps:
The client requests an access token by authenticating with the
authorization server and presenting an authorization grant.
The authorization server authenticates the client and validates
the authorization grant, and if valid, issues an access token
and optionally a refresh token.
The client makes a protected resource request to the resource
server by presenting the access token.
The resource server validates the access token, and if valid,
serves the request.
Steps (3) and (4) repeat until the access token expires. If the
client knows the access token expired, it skips to step (7);
otherwise, it makes another protected resource request.
Since the access token is invalid, the resource server returns
an invalid token error.
The client requests a new access token by presenting the refresh token
and providing client authentication if it has been issued credentials. The
client authentication requirements are based on the client type
and on the authorization server policies.
The authorization server authenticates the client and validates
the refresh token, and if valid, issues a new access token (and,
optionally, a new refresh token).
TLS VersionWhenever Transport Layer Security (TLS) is used by this
specification, the appropriate version (or versions) of TLS will vary
over time, based on the widespread deployment and known security
vulnerabilities. Refer to for up to date recommendations on
transport layer security.Implementations MAY also support additional transport-layer security
mechanisms that meet their security requirements.HTTP RedirectionsThis specification makes extensive use of HTTP redirections, in which
the client or the authorization server directs the resource owner's
user-agent to another destination. While the examples in this
specification show the use of the HTTP 302 status code, any other
method available via the user-agent to accomplish this redirection,
with the exception of HTTP 307, is allowed and is considered to be an
implementation detail. See for details.InteroperabilityOAuth 2.1 provides a rich authorization framework with well-defined
security properties.This specification leaves a few required components partially or fully
undefined (e.g., client registration, authorization server capabilities,
endpoint discovery). Some of these behaviors are defined in optional
extensions which implementations can choose to use, such as:
: Authorization Server Metadata, defining an endpoint clients can use to look up the information needed to interact with a particular OAuth server
: Dynamic Client Registration, providing a mechanism for programmatically registering clients with an authorization server
: Dynamic Client Management, providing a mechanism for updating dynamically registered client information
: Token Introspection, defining a mechanism for resource servers to obtain information about access tokens
Please refer to for a list of current known extensions at
the time of this publication.Compatibility with OAuth 2.0OAuth 2.1 is compatible with OAuth 2.0 with the extensions and restrictions
from known best current practices applied. Specifically, features not specified
in OAuth 2.0 core, such as PKCE, are required in OAuth 2.1. Additionally,
some features available in OAuth 2.0, such as the Implicit or Resource Owner Credentials
grant types, are not specified in OAuth 2.1. Furthermore, some behaviors
allowed in OAuth 2.0 are restricted in OAuth 2.1, such as the strict string
matching of redirect URIs required by OAuth 2.1.See for more details on the differences from OAuth 2.0.Notational ConventionsThe key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 when, and only when, they appear in all
capitals, as shown here.This specification uses the Augmented Backus-Naur Form (ABNF)
notation of . Additionally, the rule URI-reference is
included from "Uniform Resource Identifier (URI): Generic Syntax"
.Certain security-related terms are to be understood in the sense
defined in . These terms include, but are not limited to,
"attack", "authentication", "authorization", "certificate",
"confidentiality", "credential", "encryption", "identity", "sign",
"signature", "trust", "validate", and "verify".The term "payload" is to be interpreted as described in Section 3.3 of .Unless otherwise noted, all the protocol parameter names and values
are case sensitive.Client RegistrationBefore initiating the protocol, the client must establish its registration with the
authorization server. The means through which the client registers
with the authorization server are beyond the scope of this
specification but typically involve the client developer manually registering
the client at the authorization server's website after creating an account and agreeing
to the service's Terms of Service, or by using Dynamic Client Registration ().Client registration does not require a direct interaction between the
client and the authorization server. When supported by the
authorization server, registration can rely on other means for
establishing trust and obtaining the required client properties
(e.g., redirect URI, client type). For example, registration can
be accomplished using a self-issued or third-party-issued assertion,
or by the authorization server performing client discovery using a
trusted channel.When registering a client, the client developer SHALL:
specify the client type as described in ,
provide client details needed by the grant type in use,
such as redirect URIs as described in , and
include any other information required by the authorization server
(e.g., application name, website, description, logo image, the
acceptance of legal terms).
Dynamic Client Registration () defines a common general data model
for clients that may be used even with manual client registration.Client TypesOAuth 2.1 defines three client types based on their ability to authenticate securely
with the authorization server as well as the authorization server's assurance of the
client's identity.
"confidential":
Clients that have credentials and their identity has been confirmed by the AS are designated as "confidential clients"
"credentialed":
Clients that have credentials and their identity has been not been confirmed by the AS are designated as "credentialed clients"
"public":
Clients without credentials are called "public clients"
Any clients with credentials MUST take precautions to prevent leakage and abuse of their credentials.Authorization servers SHOULD consider the level of confidence in a client's identity
when deciding whether they allow such a client access to more critical functions,
such as the Client Credentials grant type.A single client_id MUST NOT be treated as more than one type of client.This specification has been designed around the following client profiles:
"web application":
A web application is a confidential client running on a web
server. Resource owners access the client via an HTML user
interface rendered in a user-agent on the device used by the
resource owner. The client credentials as well as any access
token issued to the client are stored on the web server and are
not exposed to or accessible by the resource owner.
"browser-based application":
A browser-based application is a public client in which the
client code is downloaded from a web server and executes within a
user-agent (e.g., web browser) on the device used by the resource
owner. Protocol data and credentials are easily accessible (and
often visible) to the resource owner. Since such applications
reside within the user-agent, they can make seamless use of the
user-agent capabilities when requesting authorization.
"native application":
A native application is a public client installed and executed on
the device used by the resource owner. Protocol data and
credentials are accessible to the resource owner. It is assumed
that any client authentication credentials included in the
application can be extracted. On the other hand, dynamically
issued credentials such as access tokens or refresh tokens can
receive an acceptable level of protection. At a minimum, these
credentials are protected from hostile servers with which the
application may interact. On some platforms, these credentials
might be protected from other applications residing on the same
device.
Client IdentifierThe authorization server issues the registered client a client
identifier - a unique string representing the registration
information provided by the client. The client identifier is not a
secret; it is exposed to the resource owner and MUST NOT be used
alone for client authentication. The client identifier is unique to
the authorization server.The client identifier string size is left undefined by this
specification. The client should avoid making assumptions about the
identifier size. The authorization server SHOULD document the size
of any identifier it issues.Authorization servers SHOULD NOT allow clients to choose or influence their
client_id value. See for details.Client AuthenticationConfidential and credentialed clients establish a client authentication method
with the authorization server suitable for the
security requirements of the authorization server. The authorization
server MAY accept any form of client authentication meeting its
security requirements.Confidential and credentialed clients are typically issued (or establish) a set of
client credentials used for authenticating with the authorization
server (e.g., password, public/private key pair).Authorization servers SHOULD use client authentication if possible.It is RECOMMENDED to use asymmetric (public-key based) methods for
client authentication such as mTLS or "private_key_jwt"
. When asymmetric methods for client authentication are
used, authorization servers do not need to store sensitive symmetric
keys, making these methods more robust against a number of attacks.The authorization server MAY establish a client authentication method
with public clients, which converts them to credentialed
clients. However, the authorization server MUST NOT rely on
credentialed client authentication for the purpose of
identifying the client.The client MUST NOT use more than one authentication method in each
request.Client SecretClients in possession of a client secret, sometimes known as a client password,
MAY use the HTTP Basic
authentication scheme as defined in to authenticate with
the authorization server. The client identifier is encoded using the
application/x-www-form-urlencoded encoding algorithm per
Appendix B, and the encoded value is used as the username; the client
secret is encoded using the same algorithm and used as the
password. The authorization server MUST support the HTTP Basic
authentication scheme for authenticating clients that were issued a
client secret.For example (with extra line breaks for display purposes only):Alternatively, the authorization server MAY support including the
client credentials in the request-body using the following
parameters:
"client_id":
REQUIRED. The client identifier issued to the client during
the registration process described by .
"client_secret":
REQUIRED. The client secret.
Including the client credentials in the request-body using the two
parameters is NOT RECOMMENDED and SHOULD be limited to clients unable
to directly utilize the HTTP Basic authentication scheme (or other
password-based HTTP authentication schemes). The parameters can only
be transmitted in the request-body and MUST NOT be included in the
request URI.For example, a request to refresh an access token () using
the body parameters (with extra line breaks for display purposes
only):The authorization server MUST require the use of TLS as described in
when sending requests using password authentication.Since this client authentication method involves a password, the
authorization server MUST protect any endpoint utilizing it against
brute force attacks.Other Authentication MethodsThe authorization server MAY support any suitable authentication
scheme matching its security requirements. When using other
authentication methods, the authorization server MUST define a
mapping between the client identifier (registration record) and
authentication scheme.Some additional authentication methods such as mTLS
and "private_key_jwt" are defined in the
"OAuth Token Endpoint Authentication Methods" registry,
and may be useful as generic client authentication methods beyond
the specific use of protecting the token endpoint.Unregistered ClientsThis specification does not exclude the use of unregistered clients.
However, the use of such clients is beyond the scope of this
specification and requires additional security analysis and review of
its interoperability impact.Protocol EndpointsThe authorization process utilizes two authorization server endpoints
(HTTP resources):
Authorization endpoint - used by the client to obtain
authorization from the resource owner via user-agent redirection.
Token endpoint - used by the client to exchange an authorization
grant for an access token, typically with client authentication.
As well as one client endpoint:
Redirection endpoint - used by the authorization server to return
responses containing authorization credentials to the client via
the resource owner user-agent.
Not every authorization grant type utilizes both endpoints.
Extension grant types MAY define additional endpoints as needed.Authorization EndpointThe authorization endpoint is used to interact with the resource
owner and obtain an authorization grant. The authorization server
MUST first verify the identity of the resource owner. The way in
which the authorization server authenticates the resource owner
(e.g., username and password login, session cookies) is beyond the
scope of this specification.The means through which the client obtains the location of the
authorization endpoint are beyond the scope of this specification,
but the location is typically provided in the service documentation,
or in the authorization server's metadata document ().The endpoint URI MAY include an "application/x-www-form-urlencoded"
formatted (per Appendix B) query component ( Section 3.4),
which MUST be retained when adding additional query parameters. The
endpoint URI MUST NOT include a fragment component.Since requests to the authorization endpoint result in user
authentication and the transmission of clear-text credentials (in the
HTTP response), the authorization server MUST require the use of TLS
as described in when sending requests to the
authorization endpoint.The authorization server MUST support the use of the HTTP GET
method for the authorization endpoint and MAY support the
use of the POST method as well.The authorization server MUST ignore unrecognized request parameters.Request and response parameters
defined by this specification MUST NOT be included more than once.
Parameters sent without a value MUST be treated as if they were
omitted from the request.Response TypeThe authorization endpoint is used by the authorization code flow.
The client informs the authorization server of the desired response type
using the following parameter:
"response_type":
REQUIRED. The value MUST be code for requesting an authorization
code as described by , or a registered extension
value as described by .
Extension response types MAY contain a space-delimited (%x20) list of
values, where the order of values does not matter (e.g., response
type a b is the same as b a). The meaning of such composite
response types is defined by their respective specifications.Some extension response types are defined by ().If an authorization request is missing the response_type parameter,
or if the response type is not understood, the authorization server
MUST return an error response as described in .Redirection EndpointAfter completing its interaction with the resource owner, the
authorization server directs the resource owner's user-agent back to
the client. The authorization server redirects the user-agent to one of the
client's redirection endpoints previously established with the
authorization server during the client registration process.The redirect URI MUST be an absolute URI as defined by
Section 4.3. The endpoint URI MAY include an
"application/x-www-form-urlencoded" formatted (per Appendix B) query
component ( Section 3.4), which MUST be retained when adding
additional query parameters. The endpoint URI MUST NOT include a
fragment component.Endpoint Request ConfidentialityThe redirection endpoint SHOULD require the use of TLS as described
in when the requested response type is code,
or when the redirection request will result in the transmission of
sensitive credentials over an open network.
If TLS is not available, the authorization server
SHOULD warn the resource owner about the insecure endpoint prior to
redirection (e.g., display a message during the authorization
request).Lack of transport-layer security can have a severe impact on the
security of the client and the protected resources it is authorized
to access. The use of transport-layer security is particularly
critical when the authorization process is used as a form of
delegated end-user authentication by the client (e.g., third-party
sign-in service).Registration RequirementsThe authorization server MUST require all clients to register one or more
complete redirect URIs prior to utilizing the authorization endpoint.
The client MAY use the state request parameter to achieve per-request
customization if needed.The authorization server MAY allow the client to register multiple
redirect URIs.Without requiring registration of redirect URIs, attackers can
use the authorization endpoint as an open redirector as
described in .Dynamic ConfigurationIf multiple redirect URIs have been registered the client MUST
include a redirect URI with the authorization request using the
redirect_uri request parameter.Invalid EndpointIf an authorization request fails validation due to a missing,
invalid, or mismatching redirect URI, the authorization server
SHOULD inform the resource owner of the error and MUST NOT
automatically redirect the user-agent to the invalid redirect URI.Endpoint ContentThe redirection request to the client's endpoint typically results in
an HTML document response, processed by the user-agent. If the HTML
response is served directly as the result of the redirection request,
any script included in the HTML document will execute with full
access to the redirect URI and the credentials (e.g. authorization code)
it contains. Additionally, the request URL containing the authorization code
may be sent in the HTTP Referer header to any embedded images, stylesheets
and other elements loaded in the page.The client SHOULD NOT include any third-party scripts (e.g., third-
party analytics, social plug-ins, ad networks) in the redirection
endpoint response. Instead, it SHOULD extract the credentials from
the URI and redirect the user-agent again to another endpoint without
exposing the credentials (in the URI or elsewhere). If third-party
scripts are included, the client MUST ensure that its own scripts
(used to extract and remove the credentials from the URI) will
execute first.Token EndpointThe token endpoint is used by the client to obtain an access token using
a grant such as those described in and
.The means through which the client obtains the location of the token
endpoint are beyond the scope of this specification, but the location
is typically provided in the service documentation and configured during
development of the client, or provided in the authorization server's metadata
document () and fetched programmatically at runtime.The endpoint URI MAY include an application/x-www-form-urlencoded
formatted (per Appendix B) query component ( Section 3.4)
and MUST NOT include a fragment component.Since requests to the token endpoint result in the transmission of
clear-text credentials (in the HTTP request and response), the
authorization server MUST require the use of TLS as described in
when sending requests to the token endpoint.The client MUST use the HTTP POST method when making access token
requests.The authorization server MUST ignore unrecognized request parameters.Parameters sent without a value MUST be treated as if they were
omitted from the request. Request and response parameters
defined by this specification MUST NOT be included more than once.Client AuthenticationConfidential clients or other clients issued client credentials MUST
authenticate with the authorization server as described in
when making requests to the token endpoint. Client
authentication is used for:
Enforcing the binding of refresh tokens and authorization codes to
the client they were issued to. Client authentication is critical
when an authorization code is transmitted to the redirection
endpoint over an insecure channel.
Recovering from a compromised client by disabling the client or
changing its credentials, thus preventing an attacker from abusing
stolen refresh tokens. Changing a single set of client
credentials is significantly faster than revoking an entire set of
refresh tokens.
Implementing authentication management best practices, which
require periodic credential rotation. Rotation of an entire set
of refresh tokens can be challenging, while rotation of a single
set of client credentials is significantly easier.
Access Token ScopeThe authorization and token endpoints allow the client to specify the
scope of the access request using the scope request parameter. In
turn, the authorization server uses the scope response parameter to
inform the client of the scope of the access token issued.The value of the scope parameter is expressed as a list of space-
delimited, case-sensitive strings. The strings are defined by the
authorization server. If the value contains multiple space-delimited
strings, their order does not matter, and each string adds an
additional access range to the requested scope.The authorization server MAY fully or partially ignore the scope
requested by the client, based on the authorization server policy or
the resource owner's instructions. If the issued access token scope
is different from the one requested by the client, the authorization
server MUST include the scope response parameter to inform the
client of the actual scope granted.If the client omits the scope parameter when requesting
authorization, the authorization server MUST either process the
request using a pre-defined default value or fail the request
indicating an invalid scope. The authorization server SHOULD
document its scope requirements and default value (if defined).Obtaining AuthorizationTo request an access token, the client obtains authorization from the
resource owner. OAuth defines two authorization grant types: authorization code
and client credentials. It also provides an extension mechanism for defining additional grant types.Authorization Code GrantThe authorization code grant type is used to obtain both access
tokens and refresh tokens.Since this is a redirect-based flow, the client must be capable of
initiating the flow with the resource owner's user-agent (typically a web
browser) and capable of being redirected back to from the authorization server.Authorization Code Flow| |
| User- | | Authorization |
| Agent -+----(2)-- User authenticates --->| Server |
| | | |
| -+----(3)-- Authorization Code ---<| |
+-|----|---+ +---------------+
| | ^ v
(1) (3) | |
| | | |
^ v | |
+---------+ | |
| |>---(4)-- Authorization Code ---------' |
| Client | & Redirect URI |
| | |
| |<---(5)----- Access Token -------------------'
+---------+ (w/ Optional Refresh Token)
Note: The lines illustrating steps (1), (2), and (3) are broken into
two parts as they pass through the user-agent.
]]>The flow illustrated in includes the following steps:(1) The client initiates the flow by directing the resource owner's
user-agent to the authorization endpoint. The client includes
its client identifier, code challenge (derived from a generated code verifier),
optional requested scope, optional local state, and a
redirect URI to which the authorization server will send the
user-agent back once access is granted (or denied).(2) The authorization server authenticates the resource owner (via
the user-agent) and establishes whether the resource owner
grants or denies the client's access request.(3) Assuming the resource owner grants access, the authorization
server redirects the user-agent back to the client using the
redirect URI provided earlier (in the request or during
client registration). The redirect URI includes an
authorization code and any local state provided by the client
earlier.(4) The client requests an access token from the authorization
server's token endpoint by including the authorization code
received in the previous step, and including its code verifier.
When making the request, the
client authenticates with the authorization server if it can. The client
includes the redirect URI used to obtain the authorization
code for verification.(5) The authorization server authenticates the client when possible, validates the
authorization code, validates the code verifier, and ensures that the redirect URI
received matches the URI used to redirect the client in
step (3). If valid, the authorization server responds back with
an access token and, optionally, a refresh token.Authorization RequestTo begin the authorization request, the client builds the authorization
request URI by adding parameters to the authorization server's
authorization endpoint URI. The client will eventually redirect the user-agent
to this URI to initiate the request, as described in .Clients use a unique secret per authorization request to protect against authorization code
injection and CSRF attacks. The client first generates this secret, which it can
use at the time of redeeming the authorization code to prove that the client using the
authorization code is the same client that requested it.Client Initiates the Authorization RequestThe client constructs the request URI by adding the following
parameters to the query component of the authorization endpoint URI
using the application/x-www-form-urlencoded format, per Appendix B:
"response_type":
REQUIRED. Value MUST be set to code.
"client_id":
REQUIRED. The client identifier as described in .
"code_challenge":
REQUIRED or RECOMMENDED (see ). Code challenge.
"code_challenge_method":
OPTIONAL, defaults to plain if not present in the request. Code
verifier transformation method is S256 or plain.
"redirect_uri":
OPTIONAL. As described in .
"scope":
OPTIONAL. The scope of the access request as described by
.
"state":
OPTIONAL. An opaque value used by the client to maintain
state between the request and callback. The authorization
server includes this value when redirecting the user-agent back
to the client.
The code_verifier is a unique high-entropy cryptographically random string generated
for each authorization request, using the unreserved characters [A-Z] / [a-z] / [0-9] / "-" / "." / "_" / "~",
with a minimum length of 43 characters and a maximum length of 128 characters.The client stores the code_verifier temporarily, and calculates the
code_challenge which it uses in the authorization request.ABNF for code_verifier is as follows.NOTE: The code verifier SHOULD have enough entropy to make it
impractical to guess the value. It is RECOMMENDED that the output of
a suitable random number generator be used to create a 32-octet
sequence. The octet sequence is then base64url-encoded to produce a
43-octet URL-safe string to use as the code verifier.The client then creates a code_challenge derived from the code
verifier by using one of the following transformations on the code
verifier:If the client is capable of using S256, it MUST use S256, as
S256 is Mandatory To Implement (MTI) on the server. Clients are
permitted to use plain only if they cannot support S256 for some
technical reason, for example constrained environments that do not have
a hashing function available, and know via out-of-band configuration or via
Authorization Server Metadata () that the server supports plain.ABNF for code_challenge is as follows.The properties code_challenge and code_verifier are adopted from the OAuth 2.0 extension
known as "Proof-Key for Code Exchange", or PKCE () where this technique
was originally developed.Clients MUST use code_challenge and code_verifier and
authorization servers MUST enforce their use except under the conditions
described in . In this case, using and enforcing
code_challenge and code_verifier as described in the following is still
RECOMMENDED.The client directs the resource owner to the constructed URI using an
HTTP redirection, or by other means available to it via the user-agent.For example, the client directs the user-agent to make the following
HTTP request using TLS (with extra line breaks for display purposes
only):The authorization server validates the request to ensure that all
required parameters are present and valid.In particular, the authorization server MUST validate the redirect_uri
in the request if present, ensuring that it matches one of the registered
redirect URIs previously established during client registration ().
When comparing the two URIs the authorization server MUST using simple
character-by-character string comparison as defined in , Section 6.2.1.If the request is valid,
the authorization server authenticates the resource owner and obtains
an authorization decision (by asking the resource owner or by
establishing approval via other means).When a decision is established, the authorization server directs the
user-agent to the provided client redirect URI using an HTTP
redirection response, or by other means available to it via the
user-agent.Authorization ResponseIf the resource owner grants the access request, the authorization
server issues an authorization code and delivers it to the client by
adding the following parameters to the query component of the
redirect URI using the application/x-www-form-urlencoded format,
per Appendix B:
"code":
REQUIRED. The authorization code generated by the
authorization server. The authorization code MUST expire
shortly after it is issued to mitigate the risk of leaks. A
maximum authorization code lifetime of 10 minutes is
RECOMMENDED. The client MUST NOT use the authorization code
more than once. If an authorization code is used more than
once, the authorization server MUST deny the request and SHOULD
revoke (when possible) all access tokens and refresh tokens previously issued based on
that authorization code. The authorization code is bound to
the client identifier and redirect URI.
"state":
REQUIRED if the state parameter was present in the client
authorization request. The exact value received from the
client.
For example, the authorization server redirects the user-agent by
sending the following HTTP response:The client MUST ignore unrecognized response parameters. The
authorization code string size is left undefined by this
specification. The client should avoid making assumptions about code
value sizes. The authorization server SHOULD document the size of
any value it issues.The authorization server MUST associate the code_challenge and
code_challenge_method values with the issued authorization code
so the code challenge can be verified later.The exact method that the server uses to associate the code_challenge
with the issued code is out of scope for this specification. The
code challenge could be stored on the server and associated with the
code there. The code_challenge and code_challenge_method values may
be stored in encrypted form in the code itself, but the server
MUST NOT include the code_challenge value in a response parameter
in a form that entities other than the AS can extract.Error ResponseIf the request fails due to a missing, invalid, or mismatching
redirect URI, or if the client identifier is missing or invalid,
the authorization server SHOULD inform the resource owner of the
error and MUST NOT automatically redirect the user-agent to the
invalid redirect URI.An AS MUST reject requests without a code_challenge from public clients,
and MUST reject such requests from other clients unless there is
reasonable assurance that the client mitigates authorization code injection
in other ways. See for details.If the server does not support the requested code_challenge_method transformation,
the authorization endpoint MUST return the
authorization error response with error value set to
invalid_request. The error_description or the response of
error_uri SHOULD explain the nature of error, e.g., transform
algorithm not supported.If the resource owner denies the access request or if the request
fails for reasons other than a missing or invalid redirect URI,
the authorization server informs the client by adding the following
parameters to the query component of the redirect URI using the
application/x-www-form-urlencoded format, per Appendix B:
"error":
REQUIRED. A single ASCII error code from the
following:
"invalid_request":
The request is missing a required parameter, includes an
invalid parameter value, includes a parameter more than
once, or is otherwise malformed.
"unauthorized_client":
The client is not authorized to request an authorization
code using this method.
"access_denied":
The resource owner or authorization server denied the
request.
"unsupported_response_type":
The authorization server does not support obtaining an
authorization code using this method.
"invalid_scope":
The requested scope is invalid, unknown, or malformed.
"server_error":
The authorization server encountered an unexpected
condition that prevented it from fulfilling the request.
(This error code is needed because a 500 Internal Server
Error HTTP status code cannot be returned to the client
via an HTTP redirect.)
"temporarily_unavailable":
The authorization server is currently unable to handle
the request due to a temporary overloading or maintenance
of the server. (This error code is needed because a 503
Service Unavailable HTTP status code cannot be returned
to the client via an HTTP redirect.)
Values for the error parameter MUST NOT include characters
outside the set %x20-21 / %x23-5B / %x5D-7E.
"error_description":
OPTIONAL. Human-readable ASCII text providing
additional information, used to assist the client developer in
understanding the error that occurred.
Values for the error_description parameter MUST NOT include
characters outside the set %x20-21 / %x23-5B / %x5D-7E.
"error_uri":
OPTIONAL. A URI identifying a human-readable web page with
information about the error, used to provide the client
developer with additional information about the error.
Values for the error_uri parameter MUST conform to the
URI-reference syntax and thus MUST NOT include characters
outside the set %x21 / %x23-5B / %x5D-7E.
"state":
REQUIRED if a state parameter was present in the client
authorization request. The exact value received from the
client.
For example, the authorization server redirects the user-agent by
sending the following HTTP response:Access Token RequestThe client makes a request to the token endpoint by sending the
following parameters using the application/x-www-form-urlencoded
format per Appendix B with a character encoding of UTF-8 in the HTTP
request payload:
"grant_type":
REQUIRED. Value MUST be set to authorization_code.
"code":
REQUIRED. The authorization code received from the
authorization server.
"redirect_uri":
REQUIRED, if the redirect_uri parameter was included in the
authorization request as described in , and their
values MUST be identical.
"client_id":
REQUIRED, if the client is not authenticating with the
authorization server as described in .
"code_verifier":
REQUIRED, if the code_challenge parameter was included in the authorization
request. MUST NOT be used otherwise. The original code verifier string.
Confidential or credentialed clients MUST authenticate with the authorization
server as described in .For example, the client makes the following HTTP request using TLS
(with extra line breaks for display purposes only):The authorization server MUST:
require client authentication for confidential and credentialed clients
(or clients with other authentication requirements),
authenticate the client if client authentication is included,
ensure that the authorization code was issued to the authenticated
confidential or credentialed client, or if the client is public, ensure that the
code was issued to client_id in the request,
verify that the authorization code is valid,
verify that the code_verifier parameter is present if and only if a
code_challenge parameter was present in the authorization request,
if a code_verifier is present, verify the code_verifier by calculating
the code challenge from the received code_verifier and comparing it with
the previously associated code_challenge, after first transforming it
according to the code_challenge_method method specified by the client, and
ensure that the redirect_uri parameter is present if the
redirect_uri parameter was included in the initial authorization
request as described in , and if included ensure that
their values are identical.
Access Token ResponseIf the access token request is valid and authorized, the
authorization server issues an access token and optional refresh
token as described in . If the request client
authentication failed or is invalid, the authorization server returns
an error response as described in .An example successful response:Client Credentials GrantThe client can request an access token using only its client
credentials (or other supported means of authentication) when the
client is requesting access to the protected resources under its
control, or those of another resource owner that have been previously
arranged with the authorization server (the method of which is beyond
the scope of this specification).The client credentials grant type MUST only be used by confidential
or credentialed clients.Client Credentials Flow--(1)- Client Authentication --->| Authorization |
| Client | | Server |
| |<--(2)---- Access Token ---------<| |
| | | |
+---------+ +---------------+
]]>The flow illustrated in includes the following steps:(1) The client authenticates with the authorization server and
requests an access token from the token endpoint.(2) The authorization server authenticates the client, and if valid,
issues an access token.Authorization Request and ResponseSince the client authentication is used as the authorization grant,
no additional authorization request is needed.Access Token RequestThe client makes a request to the token endpoint by adding the
following parameters using the application/x-www-form-urlencoded
format per Appendix B with a character encoding of UTF-8 in the HTTP
request payload:
"grant_type":
REQUIRED. Value MUST be set to client_credentials.
"scope":
OPTIONAL. The scope of the access request as described by
.
The client MUST authenticate with the authorization server as
described in .For example, the client makes the following HTTP request using
transport-layer security (with extra line breaks for display purposes
only):The authorization server MUST authenticate the client.Access Token ResponseIf the access token request is valid and authorized, the
authorization server issues an access token as described in
. A refresh token SHOULD NOT be included. If the request
failed client authentication or is invalid, the authorization server
returns an error response as described in .An example successful response:Extension GrantsThe client uses an extension grant type by specifying the grant type
using an absolute URI (defined by the authorization server) as the
value of the grant_type parameter of the token endpoint, and by
adding any additional parameters necessary.For example, to request an access token using the Device Authorization Grant
as defined by after the user has authorized the client on a separate device,
the client makes the following HTTP request using
TLS (with extra line breaks for display purposes only):If the access token request is valid and authorized, the
authorization server issues an access token and optional refresh
token as described in . If the request failed client
authentication or is invalid, the authorization server returns an
error response as described in .Issuing an Access TokenIf the access token request is valid and authorized, the
authorization server issues an access token and optional refresh
token as described in . If the request failed client
authentication or is invalid, the authorization server returns an
error response as described in .Successful ResponseThe authorization server issues an access token and optional refresh
token by creating an HTTP response body using the application/json
media type as defined by with the following parameters
and an HTTP 200 (OK) status code:
"access_token":
REQUIRED. The access token issued by the authorization server.
"token_type":
REQUIRED. The type of the access token issued as described in
. Value is case insensitive.
"expires_in":
RECOMMENDED. The lifetime in seconds of the access token. For
example, the value 3600 denotes that the access token will
expire in one hour from the time the response was generated.
If omitted, the authorization server SHOULD provide the
expiration time via other means or document the default value.
"refresh_token":
OPTIONAL. The refresh token, which can be used to obtain new
access tokens using the same authorization grant as described
in .
"scope":
OPTIONAL, if identical to the scope requested by the client;
otherwise, REQUIRED. The scope of the access token as
described by .
The parameters are serialized into a JavaScript Object Notation (JSON)
structure by adding each parameter at the highest structure level.
Parameter names and string values are included as JSON strings.
Numerical values are included as JSON numbers. The order of
parameters does not matter and can vary.The authorization server MUST include the HTTP Cache-Control
response header field with a value of no-store in any
response containing tokens, credentials, or other sensitive
information, as well as the Pragma response header field
with a value of no-cache.For example:The client MUST ignore unrecognized value names in the response. The
sizes of tokens and other values received from the authorization
server are left undefined. The client should avoid making
assumptions about value sizes. The authorization server SHOULD
document the size of any value it issues.Error ResponseThe authorization server responds with an HTTP 400 (Bad Request)
status code (unless specified otherwise) and includes the following
parameters with the response:
"error":
REQUIRED. A single ASCII error code from the following:
"invalid_request":
The request is missing a required parameter, includes an
unsupported parameter value (other than grant type),
repeats a parameter, includes multiple credentials,
utilizes more than one mechanism for authenticating the
client, contains a code_verifier although no
code_challenge was sent in the authorization request,
or is otherwise malformed.
"invalid_client":
Client authentication failed (e.g., unknown client, no
client authentication included, or unsupported
authentication method). The authorization server MAY
return an HTTP 401 (Unauthorized) status code to indicate
which HTTP authentication schemes are supported. If the
client attempted to authenticate via the Authorization
request header field, the authorization server MUST
respond with an HTTP 401 (Unauthorized) status code and
include the WWW-Authenticate response header field
matching the authentication scheme used by the client.
"invalid_grant":
The provided authorization grant (e.g., authorization
code, resource owner credentials) or refresh token is
invalid, expired, revoked, does not match the redirect
URI used in the authorization request, or was issued to
another client.
"unauthorized_client":
The authenticated client is not authorized to use this
authorization grant type.
"unsupported_grant_type":
The authorization grant type is not supported by the
authorization server.
"invalid_scope":
The requested scope is invalid, unknown, malformed, or
exceeds the scope granted by the resource owner.
Values for the error parameter MUST NOT include characters
outside the set %x20-21 / %x23-5B / %x5D-7E.
"error_description":
OPTIONAL. Human-readable ASCII text providing
additional information, used to assist the client developer in
understanding the error that occurred.
Values for the error_description parameter MUST NOT include
characters outside the set %x20-21 / %x23-5B / %x5D-7E.
"error_uri":
OPTIONAL. A URI identifying a human-readable web page with
information about the error, used to provide the client
developer with additional information about the error.
Values for the error_uri parameter MUST conform to the
URI-reference syntax and thus MUST NOT include characters
outside the set %x21 / %x23-5B / %x5D-7E.
The parameters are included in the payload of the HTTP response
using the application/json media type as defined by . The
parameters are serialized into a JSON structure by adding each
parameter at the highest structure level. Parameter names and string
values are included as JSON strings. Numerical values are included
as JSON numbers. The order of parameters does not matter and can
vary.For example:Refreshing an Access TokenAuthorization servers SHOULD determine, based on a risk assessment
and their own policies, whether to issue refresh tokens to a certain client. If the
authorization server decides not to issue refresh tokens, the client
MAY obtain new access tokens by starting the OAuth flow over, for example
initiating a new authorization code request. In such a case, the authorization
server may utilize cookies and persistent grants to optimize the user
experience.If refresh tokens are issued, those refresh tokens MUST be bound to
the scope and resource servers as consented by the resource owner.
This is to prevent privilege escalation by the legitimate client and
reduce the impact of refresh token leakage.Refresh Token RequestTo use a refresh token to obtain a new access token, the
client makes a request to the token endpoint by adding the
following parameters using the application/x-www-form-urlencoded
format (per Appendix B) with a character encoding of UTF-8 in the HTTP
request payload:
"grant_type":
REQUIRED. Value MUST be set to refresh_token.
"refresh_token":
REQUIRED. The refresh token issued to the client.
"scope":
OPTIONAL. The scope of the access request as described by
. The requested scope MUST NOT include any scope
not originally granted by the resource owner, and if omitted is
treated as equal to the scope originally granted by the
resource owner.
Because refresh tokens are typically long-lasting credentials used to
request additional access tokens, the refresh token is bound to the
client to which it was issued. Confidential or credentialed clients
MUST authenticate with the authorization server as described in
.For example, the client makes the following HTTP request using
transport-layer security (with extra line breaks for display purposes
only):The authorization server MUST:
require client authentication for confidential or credentialed clients
authenticate the client if client authentication is included and
ensure that the refresh token was issued to the authenticated
client, and
validate the refresh token.
Authorization servers SHOULD utilize one of these methods to detect
refresh token replay by malicious actors for public clients:
Sender-constrained refresh tokens: the authorization server
cryptographically binds the refresh token to a certain client
instance by utilizing , ,
, or another suitable method.
Refresh token rotation: the authorization server issues a new
refresh token with every access token refresh response. The
previous refresh token is invalidated but information about the
relationship is retained by the authorization server. If a
refresh token is compromised and subsequently used by both the
attacker and the legitimate client, one of them will present an
invalidated refresh token, which will inform the authorization
server of the breach. The authorization server cannot determine
which party submitted the invalid refresh token, but it will
revoke the active refresh token. This stops the attack at the
cost of forcing the legitimate client to obtain a fresh
authorization grant.
Implementation note: the grant to which a refresh token belongs
may be encoded into the refresh token itself. This can enable an
authorization server to efficiently determine the grant to which a
refresh token belongs, and by extension, all refresh tokens that
need to be revoked. Authorization servers MUST ensure the
integrity of the refresh token value in this case, for example,
using signatures.Refresh Token ResponseIf valid and authorized, the authorization server issues an access
token as described in . If the request failed
verification or is invalid, the authorization server returns an error
response as described in .The authorization server MAY issue a new refresh token, in which case
the client MUST discard the old refresh token and replace it with the
new refresh token. The authorization server MAY revoke the old
refresh token after issuing a new refresh token to the client. If a
new refresh token is issued, the refresh token scope MUST be
identical to that of the refresh token included by the client in the
request.Authorization servers MAY revoke refresh tokens automatically in case
of a security event, such as:
password change
logout at the authorization server
Refresh tokens SHOULD expire if the client has been inactive for some
time, i.e., the refresh token has not been used to obtain new
access tokens for some time. The expiration time is at the
discretion of the authorization server. It might be a global value
or determined based on the client policy or the grant associated with
the refresh token (and its sensitivity).Accessing Protected ResourcesThe client accesses protected resources by presenting the access
token to the resource server. The resource server MUST validate the
access token and ensure that it has not expired and that its scope
covers the requested resource. The methods used by the resource
server to validate the access token (as well as any error responses)
are beyond the scope of this specification, but generally involve an
interaction or coordination between the resource server and the
authorization server, such as using Token Introspection
or a structured access token format such as a JWT .The method in which the client utilizes the access token to
authenticate with the resource server depends on the type of access
token issued by the authorization server. Typically, it involves
using the HTTP Authorization request header field with an
authentication scheme defined by the specification of the access
token type used, such as Bearer, defined below.Access Token TypesThe access token type provides the client with the information
required to successfully utilize the access token to make a protected
resource request (along with type-specific attributes). The client
MUST NOT use an access token if it does not understand the token
type.For example, the Bearer token type defined in this specification is utilized
by simply including the access token string in the request:The above example is provided for illustration purposes only.Each access token type definition specifies the additional attributes
(if any) sent to the client together with the access_token response
parameter. It also defines the HTTP authentication method used to
include the access token when making a protected resource request.Bearer TokensA Bearer Token is a security token with the property that any party
in possession of the token (a "bearer") can use the token in any way
that any other party in possession of it can. Using a bearer token
does not require a bearer to prove possession of cryptographic key material
(proof-of-possession).Bearer tokens may be extended to include proof-of-possession techniques
by other specifications.Authenticated RequestsThis section defines two methods of sending Bearer tokens in resource
requests to resource servers. Clients MUST NOT use more than one method
to transmit the token in each request.Authorization Request Header FieldWhen sending the access token in the Authorization request header
field defined by HTTP/1.1 , the client uses the Bearer
authentication scheme to transmit the access token.For example:The syntax of the Authorization header field for this scheme
follows the usage of the Basic scheme defined in Section 2 of
. Note that, as with Basic, it does not conform to the
generic syntax defined in Section 1.2 of but is compatible
with the general authentication framework in HTTP 1.1 Authentication
, although it does not follow the preferred
practice outlined therein in order to reflect existing deployments.
The syntax for Bearer credentials is as follows:Clients SHOULD make authenticated requests with a bearer token using
the Authorization request header field with the Bearer HTTP
authorization scheme. Resource servers MUST support this method.Form-Encoded Body ParameterWhen sending the access token in the HTTP request payload, the
client adds the access token to the request-body using the
access_token parameter. The client MUST NOT use this method unless
all of the following conditions are met:
The HTTP request entity-header includes the Content-Type header
field set to application/x-www-form-urlencoded.
The payload follows the encoding requirements of the
application/x-www-form-urlencoded content-type as defined by
HTML 4.01 .
The HTTP request payload is single-part.
The content to be encoded in the payload MUST consist entirely
of ASCII characters.
The HTTP request method is one for which the request-body has
defined semantics. In particular, this means that the GET
method MUST NOT be used.
The payload MAY include other request-specific parameters, in
which case the access_token parameter MUST be properly separated
from the request-specific parameters using & character(s) (ASCII
code 38).For example, the client makes the following HTTP request using
transport-layer security:The application/x-www-form-urlencoded method SHOULD NOT be used
except in application contexts where participating clients do not
have access to the Authorization request header field. Resource
servers MAY support this method.The WWW-Authenticate Response Header FieldIf the protected resource request does not include authentication
credentials or does not contain an access token that enables access
to the protected resource, the resource server MUST include the HTTP
WWW-Authenticate response header field; it MAY include it in
response to other conditions as well. The WWW-Authenticate header
field uses the framework defined by HTTP/1.1 .All challenges defined by this specification MUST use the auth-scheme
value Bearer. This scheme MUST be followed by one or more
auth-param values. The auth-param attributes used or defined by this
specification are as follows. Other auth-param attributes MAY be
used as well.A realm attribute MAY be included to indicate the scope of
protection in the manner described in HTTP/1.1 . The
realm attribute MUST NOT appear more than once.The scope attribute is defined in . The
scope attribute is a space-delimited list of case-sensitive scope
values indicating the required scope of the access token for
accessing the requested resource. scope values are implementation
defined; there is no centralized registry for them; allowed values
are defined by the authorization server. The order of scope values
is not significant. In some cases, the scope value will be used
when requesting a new access token with sufficient scope of access to
utilize the protected resource. Use of the scope attribute is
OPTIONAL. The scope attribute MUST NOT appear more than once. The
scope value is intended for programmatic use and is not meant to be
displayed to end-users.Two example scope values follow; these are taken from the OpenID
Connect and the Open Authentication Technology
Committee (OATC) Online Multimedia Authorization Protocol
OAuth 2.0 use cases, respectively:If the protected resource request included an access token and failed
authentication, the resource server SHOULD include the error
attribute to provide the client with the reason why the access
request was declined. The parameter value is described in
. In addition, the resource server MAY include the
error_description attribute to provide developers a human-readable
explanation that is not meant to be displayed to end-users. It also
MAY include the error_uri attribute with an absolute URI
identifying a human-readable web page explaining the error. The
error, error_description, and error_uri attributes MUST NOT
appear more than once.Values for the scope attribute (specified in Appendix A.4)
MUST NOT include characters outside the set %x21 / %x23-5B
/ %x5D-7E for representing scope values and %x20 for delimiters
between scope values. Values for the error and error_description
attributes (specified in Appendixes A.7 and A.8) MUST
NOT include characters outside the set %x20-21 / %x23-5B / %x5D-7E.
Values for the error_uri attribute (specified in Appendix A.9 of)
MUST conform to the URI-reference syntax and thus MUST NOT
include characters outside the set %x21 / %x23-5B / %x5D-7E.For example, in response to a protected resource request without
authentication:And in response to a protected resource request with an
authentication attempt using an expired access token:Error CodesWhen a request fails, the resource server responds using the
appropriate HTTP status code (typically, 400, 401, 403, or 405) and
includes one of the following error codes in the response:
"invalid_request":
The request is missing a required parameter, includes an
unsupported parameter or parameter value, repeats the same
parameter, uses more than one method for including an access
token, or is otherwise malformed. The resource server SHOULD
respond with the HTTP 400 (Bad Request) status code.
"invalid_token":
The access token provided is expired, revoked, malformed, or
invalid for other reasons. The resource SHOULD respond with
the HTTP 401 (Unauthorized) status code. The client MAY
request a new access token and retry the protected resource
request.
"insufficient_scope":
The request requires higher privileges than provided by the
access token. The resource server SHOULD respond with the HTTP
403 (Forbidden) status code and MAY include the scope
attribute with the scope necessary to access the protected
resource.
If the request lacks any authentication information (e.g., the client
was unaware that authentication is necessary or attempted using an
unsupported authentication method), the resource server SHOULD NOT
include an error code or other error information.For example:Error ResponseIf a resource access request fails, the resource server SHOULD inform
the client of the error. The method by which the resource server
does this is determined by the particular token type, such as the
description of Bearer tokens in .Extension Token Types establishes a common registry in Section 11.4
for error values to be shared among OAuth token authentication schemes.New authentication schemes designed primarily for OAuth token
authentication SHOULD define a mechanism for providing an error
status code to the client, in which the error values allowed are
registered in the error registry established by this specification.Such schemes MAY limit the set of valid error codes to a subset of
the registered values. If the error code is returned using a named
parameter, the parameter name SHOULD be error.Other schemes capable of being used for OAuth token authentication,
but not primarily designed for that purpose, MAY bind their error
values to the registry in the same manner.New authentication schemes MAY choose to also specify the use of the
error_description and error_uri parameters to return error
information in a manner parallel to their usage in this
specification.Access Token Security ConsiderationsSecurity ThreatsThe following list presents several common threats against protocols
utilizing some form of tokens. This list of threats is based on NIST
Special Publication 800-63 .Token manufacture/modificationAn attacker may generate a bogus
token or modify the token contents (such as the authentication or
attribute statements) of an existing token, causing the resource
server to grant inappropriate access to the client. For example,
an attacker may modify the token to extend the validity period; a
malicious client may modify the assertion to gain access to
information that they should not be able to view.Token disclosureTokens may contain authentication and attribute
statements that include sensitive information.Token redirectAn attacker uses a token generated for consumption
by one resource server to gain access to a different resource
server that mistakenly believes the token to be for it.Token replayAn attacker attempts to use a token that has already
been used with that resource server in the past.Threat MitigationA large range of threats can be mitigated by protecting the contents
of the token by using a digital signature.
Alternatively, a bearer token can contain a reference to
authorization information, rather than encoding the information
directly. Such references MUST be infeasible for an attacker to
guess; using a reference may require an extra interaction between a
server and the token issuer to resolve the reference to the
authorization information. The mechanics of such an interaction are
not defined by this specification.This document does not specify the encoding or the contents of the
token; hence, detailed recommendations about the means of
guaranteeing token integrity protection are outside the scope of this
document. The token integrity protection MUST be sufficient to
prevent the token from being modified.To deal with token redirect, it is important for the authorization
server to include the identity of the intended recipients (the
audience), typically a single resource server (or a list of resource
servers), in the token. Restricting the use of the token to a
specific scope is also RECOMMENDED.The authorization server MUST implement TLS. Which version(s) ought
to be implemented will vary over time and will depend on the
widespread deployment and known security vulnerabilities at the time
of implementation.To protect against token disclosure, confidentiality protection MUST
be applied using TLS with a ciphersuite that provides
confidentiality and integrity protection. This requires that the
communication interaction between the client and the authorization
server, as well as the interaction between the client and the
resource server, utilize confidentiality and integrity protection.
Since TLS is mandatory to implement and to use with this
specification, it is the preferred approach for preventing token
disclosure via the communication channel. For those cases where the
client is prevented from observing the contents of the token, token
encryption MUST be applied in addition to the usage of TLS
protection. As a further defense against token disclosure, the
client MUST validate the TLS certificate chain when making requests
to protected resources, including checking the Certificate Revocation
List (CRL) .Cookies are typically transmitted in the clear. Thus, any
information contained in them is at risk of disclosure. Therefore,
Bearer tokens MUST NOT be stored in cookies that can be sent in the
clear, as any information in them is at risk of disclosure.
See "HTTP State Management Mechanism" for security
considerations about cookies.In some deployments, including those utilizing load balancers, the
TLS connection to the resource server terminates prior to the actual
server that provides the resource. This could leave the token
unprotected between the front-end server where the TLS connection
terminates and the back-end server that provides the resource. In
such deployments, sufficient measures MUST be employed to ensure
confidentiality of the token between the front-end and back-end
servers; encryption of the token is one such possible measure.To deal with token capture and replay, the following recommendations
are made: First, the lifetime of the token MUST be limited; one means
of achieving this is by putting a validity time field inside the
protected part of the token. Note that using short-lived (one hour
or less) tokens reduces the impact of them being leaked. Second,
confidentiality protection of the exchanges between the client and
the authorization server and between the client and the resource
server MUST be applied. As a consequence, no eavesdropper along the
communication path is able to observe the token exchange.
Consequently, such an on-path adversary cannot replay the token.
Furthermore, when presenting the token to a resource server, the
client MUST verify the identity of that resource server, as per
Section 3.1 of "HTTP Over TLS" . Note that the client MUST
validate the TLS certificate chain when making these requests to
protected resources. Presenting the token to an unauthenticated and
unauthorized resource server or failing to validate the certificate
chain will allow adversaries to steal the token and gain unauthorized
access to protected resources.Summary of RecommendationsSafeguard bearer tokensClient implementations MUST ensure that
bearer tokens are not leaked to unintended parties, as they will
be able to use them to gain access to protected resources. This
is the primary security consideration when using bearer tokens and
underlies all the more specific recommendations that follow.Validate TLS certificate chainsThe client MUST validate the TLS
certificate chain when making requests to protected resources.
Failing to do so may enable DNS hijacking attacks to steal the
token and gain unintended access.Always use TLS (https)Clients MUST always use TLS
(https) or equivalent transport security when making requests with
bearer tokens. Failing to do so exposes the token to numerous
attacks that could give attackers unintended access.Don't store bearer tokens in HTTP cookiesImplementations MUST NOT store
bearer tokens within cookies that can be sent in the clear (which
is the default transmission mode for cookies). Implementations
that do store bearer tokens in cookies MUST take precautions
against cross-site request forgery.Issue short-lived bearer tokensAuthorization servers SHOULD issue
short-lived (one hour or less) bearer tokens, particularly when
issuing tokens to clients that run within a web browser or other
environments where information leakage may occur. Using
short-lived bearer tokens can reduce the impact of them being
leaked.Issue scoped bearer tokensAuthorization servers SHOULD issue bearer tokens
that contain an audience restriction, scoping their use to the
intended relying party or set of relying parties.Don't pass bearer tokens in page URLsBearer tokens MUST NOT be
passed in page URLs (for example, as query string parameters).
Instead, bearer tokens SHOULD be passed in HTTP message headers or
message bodies for which confidentiality measures are taken.
Browsers, web servers, and other software may not adequately
secure URLs in the browser history, web server logs, and other
data structures. If bearer tokens are passed in page URLs,
attackers might be able to steal them from the history data, logs,
or other unsecured locations.Token Replay PreventionA sender-constrained access token scopes the applicability of an
access token to a certain sender. This sender is obliged to
demonstrate knowledge of a certain secret as prerequisite for the
acceptance of that access token at the recipient (e.g., a resource server).Authorization and resource servers SHOULD use mechanisms for sender-
constrained access tokens to prevent token replay as described in
Section 4.8.1.1.2 of .
The use of Mutual TLS for OAuth 2.0 is RECOMMENDED.It is RECOMMENDED to use end-to-end TLS. If TLS traffic needs to be
terminated at an intermediary, refer to Section 4.11 of
for further security advice.Access Token Privilege RestrictionThe privileges associated with an access token SHOULD be restricted
to the minimum required for the particular application or use case.
This prevents clients from exceeding the privileges authorized by the
resource owner. It also prevents users from exceeding their
privileges authorized by the respective security policy. Privilege
restrictions also help to reduce the impact of access token leakage.In particular, access tokens SHOULD be restricted to certain resource
servers (audience restriction), preferably to a single resource
server. To put this into effect, the authorization server associates
the access token with certain resource servers and every resource
server is obliged to verify, for every request, whether the access
token sent with that request was meant to be used for that particular
resource server. If not, the resource server MUST refuse to serve
the respective request. Clients and authorization servers MAY
utilize the parameters scope or resource as specified in
this document and , respectively, to
determine the resource server they want to access.Additionally, access tokens SHOULD be restricted to certain resources
and actions on resource servers or resources. To put this into
effect, the authorization server associates the access token with the
respective resource and actions and every resource server is obliged
to verify, for every request, whether the access token sent with that
request was meant to be used for that particular action on the
particular resource. If not, the resource server must refuse to
serve the respective request. Clients and authorization servers MAY
utilize the parameter scope and
authorization_details as specified in to
determine those resources and/or actions.ExtensibilityDefining Access Token TypesAccess token types can be defined in one of two ways: registered in
the Access Token Types registry (following the procedures in
Section 11.1 of ), or by using a unique absolute URI as its name.Types utilizing a URI name SHOULD be limited to vendor-specific
implementations that are not commonly applicable, and are specific to
the implementation details of the resource server where they are
used.All other types MUST be registered. Type names MUST conform to the
type-name ABNF. If the type definition includes a new HTTP
authentication scheme, the type name SHOULD be identical to the HTTP
authentication scheme name (as defined by ). The token type
example is reserved for use in examples.Defining New Endpoint ParametersNew request or response parameters for use with the authorization
endpoint or the token endpoint are defined and registered in the
OAuth Parameters registry following the procedure in Section 11.2 of .Parameter names MUST conform to the param-name ABNF, and parameter
values syntax MUST be well-defined (e.g., using ABNF, or a reference
to the syntax of an existing parameter).Unregistered vendor-specific parameter extensions that are not
commonly applicable and that are specific to the implementation
details of the authorization server where they are used SHOULD
utilize a vendor-specific prefix that is not likely to conflict with
other registered values (e.g., begin with 'companyname_').Defining New Authorization Grant TypesNew authorization grant types can be defined by assigning them a
unique absolute URI for use with the grant_type parameter. If the
extension grant type requires additional token endpoint parameters,
they MUST be registered in the OAuth Parameters registry as described
by Section 11.2 of .Defining New Authorization Endpoint Response TypesNew response types for use with the authorization endpoint are
defined and registered in the Authorization Endpoint Response Types
registry following the procedure in Section 11.3 of . Response type
names MUST conform to the response-type ABNF.If a response type contains one or more space characters (%x20), it
is compared as a space-delimited list of values in which the order of
values does not matter. Only one order of values can be registered,
which covers all other arrangements of the same set of values.For example, an extension can define and register the code other_token
response type. Once registered, the same combination cannot be registered
as other_token code, but both values can be used to
denote the same response type.Defining Additional Error CodesIn cases where protocol extensions (i.e., access token types,
extension parameters, or extension grant types) require additional
error codes to be used with the authorization code grant error
response (), the token error response (), or the
resource access error response (), such error codes MAY be
defined.Extension error codes MUST be registered (following the procedures in
Section 11.4 of ) if the extension they are used in conjunction with is a
registered access token type, a registered endpoint parameter, or an
extension grant type. Error codes used with unregistered extensions
MAY be registered.Error codes MUST conform to the error ABNF and SHOULD be prefixed by
an identifying name when possible. For example, an error identifying
an invalid value set to the extension parameter example SHOULD be
named example_invalid.Security ConsiderationsAs a flexible and extensible framework, OAuth's security
considerations depend on many factors. The following sections
provide implementers with security guidelines focused on the three
client profiles described in : web application,
browser-based application, and native application.A comprehensive OAuth security model and analysis, as well as
background for the protocol design, is provided by
and .Client AuthenticationAuthorization servers SHOULD use client authentication if possible.It is RECOMMENDED to use asymmetric (public-key based) methods for
client authentication such as mTLS or
private_key_jwt. When asymmetric methods for client
authentication are used, authorization servers do not need to store
sensitive symmetric keys, making these methods more robust against a
number of attacks.Authorization server MUST only rely on client authentication if the
process of issuance/registration and distribution of the underlying
credentials ensures their confidentiality.When client authentication is not possible, the authorization server
SHOULD employ other means to validate the client's identity - for
example, by requiring the registration of the client redirect URI
or enlisting the resource owner to confirm identity. A valid
redirect URI is not sufficient to verify the client's identity
when asking for resource owner authorization but can be used to
prevent delivering credentials to a counterfeit client after
obtaining resource owner authorization.The authorization server must consider the security implications of
interacting with unauthenticated clients and take measures to limit
the potential exposure of other credentials (e.g., refresh tokens)
issued to such clients.The privileges an authorization server associates with a certain
client identity MUST depend on the assessment of the overall process
for client identification and client credential lifecycle management.
For example, authentication of a dynamically registered client just
ensures the authorization server it is talking to the same client again.
In contrast, if there is a web application whose developer's identity
was verified, who signed a contract and is issued a client secret
that is only used in a secure backend service, the authorization
server might allow this client to access more sensible services
or to use the client credential grant type.Client Authentication of Native AppsSecrets that are statically included as part of an app distributed to
multiple users should not be treated as confidential secrets, as one
user may inspect their copy and learn the shared secret. For this
reason, it is NOT
RECOMMENDED for authorization servers to require client
authentication of public native apps clients using a shared secret,
as this serves little value beyond client identification which is
already provided by the client_id request parameter.Authorization servers that still require a statically included shared
secret for native app clients MUST treat the client as a public
client (as defined in ), and not
accept the secret as proof of the client's identity. Without
additional measures, such clients are subject to client impersonation
(see ).Registration of Native App ClientsExcept when using a mechanism like Dynamic Client Registration
to provision per-instance secrets, native apps are
classified as public clients, as defined in ;
they MUST be registered with the authorization server as
such. Authorization servers MUST record the client type in the
client registration details in order to identify and process requests
accordingly.Authorization servers MUST require clients to register their complete
redirect URI (including the path component) and reject authorization
requests that specify a redirect URI that doesn't exactly match the
one that was registered; the exception is loopback redirects, where
an exact match is required except for the port URI component.For private-use URI scheme-based redirects, authorization servers
SHOULD enforce the requirement in that clients use
schemes that are reverse domain name based. At a minimum, any
private-use URI scheme that doesn't contain a period character (.)
SHOULD be rejected.In addition to the collision-resistant properties, requiring a URI
scheme based on a domain name that is under the control of the app
can help to prove ownership in the event of a dispute where two apps
claim the same private-use URI scheme (where one app is acting
maliciously). For example, if two apps claimed com.example.app,
the owner of example.com could petition the app store operator to
remove the counterfeit app. Such a petition is harder to prove if a
generic URI scheme was used.Authorization servers MAY request the inclusion of other platform-
specific information, such as the app package or bundle name, or
other information that may be useful for verifying the calling app's
identity on operating systems that support such functions.Client ImpersonationA malicious client can impersonate another client and obtain access
to protected resources if the impersonated client fails to, or is
unable to, keep its client credentials confidential.The authorization server MUST authenticate the client whenever
possible. If the authorization server cannot authenticate the client
due to the client's nature, the authorization server MUST require the
registration of any redirect URI used for receiving authorization
responses and SHOULD utilize other means to protect resource owners
from such potentially malicious clients. For example, the
authorization server can engage the resource owner to assist in
identifying the client and its origin.The authorization server SHOULD enforce explicit resource owner
authentication and provide the resource owner with information about
the client and the requested authorization scope and lifetime. It is
up to the resource owner to review the information in the context of
the current client and to authorize or deny the request.The authorization server SHOULD NOT process repeated authorization
requests automatically (without active resource owner interaction)
without authenticating the client or relying on other measures to
ensure that the repeated request comes from the original client and
not an impersonator.Impersonation of Native AppsAs stated above, the authorization
server SHOULD NOT process authorization requests automatically
without user consent or interaction, except when the identity of the
client can be assured. This includes the case where the user has
previously approved an authorization request for a given client id -
unless the identity of the client can be proven, the request SHOULD
be processed as if no previous request had been approved.Measures such as claimed https scheme redirects MAY be accepted by
authorization servers as identity proof. Some operating systems may
offer alternative platform-specific identity features that MAY be
accepted, as appropriate.Access TokensAccess token credentials (as well as any confidential access token
attributes) MUST be kept confidential in transit and storage, and
only shared among the authorization server, the resource servers the
access token is valid for, and the client to whom the access token is
issued. Access token credentials MUST only be transmitted using TLS
as described in with server authentication as defined by
.The authorization server MUST ensure that access tokens cannot be
generated, modified, or guessed to produce valid access tokens by
unauthorized parties.Access Token Privilege RestrictionThe client SHOULD request access tokens with the minimal scope
necessary. The authorization server SHOULD take the client identity
into account when choosing how to honor the requested scope and MAY
issue an access token with less rights than requested.The privileges associated with an access token SHOULD be restricted to
the minimum required for the particular application or use case. This
prevents clients from exceeding the privileges authorized by the
resource owner. It also prevents users from exceeding their privileges
authorized by the respective security policy. Privilege restrictions
also help to reduce the impact of access token leakage.In particular, access tokens SHOULD be restricted to certain resource
servers (audience restriction), preferably to a single resource
server. To put this into effect, the authorization server associates
the access token with certain resource servers and every resource
server is obliged to verify, for every request, whether the access
token sent with that request was meant to be used for that particular
resource server. If not, the resource server MUST refuse to serve the
respective request. Clients and authorization servers MAY utilize the
parameters scope or resource as specified in
, respectively, to determine the
resource server they want to access.Access Token Replay PreventionAdditionally, access tokens SHOULD be restricted to certain resources
and actions on resource servers or resources. To put this into effect,
the authorization server associates the access token with the
respective resource and actions and every resource server is obliged
to verify, for every request, whether the access token sent with that
request was meant to be used for that particular action on the
particular resource. If not, the resource server must refuse to serve
the respective request. Clients and authorization servers MAY utilize
the parameter scope and authorization_details as specified in
to determine those resources and/or actions.Authorization and resource servers SHOULD use mechanisms for
sender-constrained access tokens to prevent token replay as described
in (#pop_tokens). A sender-constrained access token scopes the applicability
of an access
token to a certain sender. This sender is obliged to demonstrate knowledge
of a certain secret as prerequisite for the acceptance of that access token at
the recipient (e.g., a resource server). The use of Mutual TLS for OAuth 2.0
is RECOMMENDED.Refresh TokensAuthorization servers MAY issue refresh tokens to clients.Refresh tokens MUST be kept confidential in transit and storage, and
shared only among the authorization server and the client to whom the
refresh tokens were issued. The authorization server MUST maintain
the binding between a refresh token and the client to whom it was
issued. Refresh tokens MUST only be transmitted using TLS as
described in with server authentication as defined by
.The authorization server MUST verify the binding between the refresh
token and client identity whenever the client identity can be
authenticated. When client authentication is not possible, the
authorization server SHOULD issue sender-constrained refresh tokens
or use refresh token rotation as described in (#refreshing-an-access-token).The authorization server MUST ensure that refresh tokens cannot be
generated, modified, or guessed to produce valid refresh tokens by
unauthorized parties.Client Impersonating Resource OwnerResource servers may make access control decisions based on the
identity of the resource owner as communicated in the sub claim
returned by the authorization server in a token introspection
response or other mechanisms. If a client is able to
choose its own client_id during registration with the authorization
server, then there is a risk that it can register with the same sub
value as a privileged user. A subsequent access token obtained under
the client credentials grant may be mistaken for an access token
authorized by the privileged user if the resource server does not
perform additional checks.Authorization servers SHOULD NOT allow clients to influence their
client_id or sub value or any other claim if that can cause
confusion with a genuine resource owner. Where this cannot be
avoided, authorization servers MUST provide other means for the
resource server to distinguish between access tokens authorized by a
resource owner from access tokens authorized by the client itself.Protecting Redirect-Based FlowsWhen comparing client redirect URIs against pre-registered URIs,
authorization servers MUST utilize exact string matching. This measure
contributes to the prevention of leakage of authorization codes and
access tokens (see (#insufficient_uri_validation)). It can also help to
detect mix-up attacks (see (#mix_up)).Clients MUST NOT expose URLs that forward the user's browser to
arbitrary URIs obtained from a query parameter ("open redirector").
Open redirectors can enable exfiltration of authorization codes and
access tokens, see (#open_redirector_on_client).Clients MUST prevent Cross-Site Request Forgery (CSRF). In this
context, CSRF refers to requests to the redirection endpoint that do
not originate at the authorization server, but a malicious third party
(see Section 4.4.1.8. of for details). Clients that have
ensured that the authorization server supports the code_challenge parameter MAY
rely the CSRF protection provided by that mechanism. In OpenID Connect flows,
the nonce parameter provides CSRF protection. Otherwise, one-time
use CSRF tokens carried in the state parameter that are securely
bound to the user agent MUST be used for CSRF protection (see
(#csrf_countermeasures)).In order to prevent mix-up attacks (see (#mix_up)), clients MUST only process redirect
responses of the authorization server they sent the respective request
to and from the same user agent this authorization request was
initiated with. Clients MUST store the authorization server they sent
an authorization request to and bind this information to the user
agent and check that the authorization request was received from the
correct authorization server. Clients MUST ensure that the subsequent
access token request, if applicable, is sent to the same authorization
server. Clients SHOULD use distinct redirect URIs for each
authorization server as a means to identify the authorization server a
particular response came from.An AS that redirects a request potentially containing user credentials
MUST avoid forwarding these user credentials accidentally (see
for details).Loopback Redirect Considerations in Native AppsLoopback interface redirect URIs use the http scheme (i.e., without
Transport Layer Security (TLS)). This is acceptable for loopback
interface redirect URIs as the HTTP request never leaves the device.Clients should open the network port only when starting the
authorization request and close it once the response is returned.Clients should listen on the loopback network interface only, in
order to avoid interference by other network actors.While redirect URIs using localhost (i.e.,
http://localhost:{port}/{path}) function similarly to loopback IP
redirects described in , the use of localhost is NOT
RECOMMENDED. Specifying a redirect URI with the loopback IP literal
rather than localhost avoids inadvertently listening on network
interfaces other than the loopback interface. It is also less
susceptible to client-side firewalls and misconfigured host name
resolution on the user's device.HTTP 307 RedirectAn AS which redirects a request that potentially contains user
credentials MUST NOT use the HTTP 307 status code for
redirection. If an HTTP redirection (and not, for example,
JavaScript) is used for such a request, AS SHOULD use HTTP status
code 303 "See Other".At the authorization endpoint, a typical protocol flow is that the AS
prompts the user to enter their credentials in a form that is then
submitted (using the HTTP POST method) back to the authorization
server. The AS checks the credentials and, if successful, redirects
the user agent to the client's redirect URI.If the status code 307 were used for redirection, the user agent
would send the user credentials via HTTP POST to the client.This discloses the sensitive credentials to the client. If the
relying party is malicious, it can use the credentials to impersonate
the user at the AS.The behavior might be unexpected for developers, but is defined in
, Section 6.4.7. This status code does not require the user
agent to rewrite the POST request to a GET request and thereby drop
the form data in the POST request body.In the HTTP standard , only the status code 303
unambigiously enforces rewriting the HTTP POST request to an HTTP GET
request. For all other status codes, including the popular 302, user
agents can opt not to rewrite POST to GET requests and therefore to
reveal the user credentials to the client. (In practice, however,
most user agents will only show this behaviour for 307 redirects.)Therefore, the RECOMMENDED status code for HTTP redirects is 303.Authorization CodesThe transmission of authorization codes MUST be made over a secure
channel, and the client MUST require the use of TLS with its
redirect URI if the URI identifies a network resource. Since
authorization codes are transmitted via user-agent redirections, they
could potentially be disclosed through user-agent history and HTTP
referrer headers.Authorization codes MUST be short lived and single-use. If the
authorization server observes multiple attempts to exchange an
authorization code for an access token, the authorization server
SHOULD attempt to revoke all refresh and access tokens already granted
based on the compromised authorization code.If the client can be authenticated, the authorization servers MUST
authenticate the client and ensure that the authorization code was
issued to the same client.Clients MUST prevent injection (replay) of authorization codes into the
authorization response by attackers. To this end, using code_challenge and
code_verifier is REQUIRED for clients and authorization servers MUST enforce
their use, unless both of the following criteria are met:
The client is a confidential client.
In the specific deployment and the specific request, there is reasonable
assurance for authorization server that the client implements the OpenID
Connect nonce mechanism properly.
In this case, using and enforcing code_challenge and code_verifier is still RECOMMENDED.The code_challenge or OpenID Connect nonce value MUST be
transaction-specific and securely bound to the client and the user agent in
which the transaction was started. If a transaction leads to an error, fresh
values for code_challenge or nonce MUST be chosen.Historic note: Although PKCE was originally designed as a mechanism
to protect native apps, this advice applies to all kinds of OAuth clients,
including web applications and other confidential clients.Clients SHOULD use code challenge methods that
do not expose the code_verifier in the authorization request.
Otherwise, attackers that can read the authorization request (cf.
Attacker A4 in (#secmodel)) can break the security provided
by this mechanism. Currently, S256 is the only such method.When an authorization code arrives at the token endpoint, the
authorization server MUST do the following check:
If there was a code_challenge in the authorization request for which this
code was issued, there must be a code_verifier in the token request, and it
MUST be verified according to the steps in .
(This is no change from the current behavior in .)
If there was no code_challenge in the authorization request, any request to
the token endpoint containing a code_verifier MUST be rejected.
Authorization servers MUST support the code_challenge and code_verifier parameters.Authorization servers MUST provide a way to detect their support for
the code_challenge mechanism. To this end, they MUST either (a) publish the element
code_challenge_methods_supported in their AS metadata ()
containing the supported code_challenge_methods (which can be used by
the client to detect support) or (b) provide a
deployment-specific way to ensure or determine support by the AS.Request ConfidentialityAccess tokens, refresh tokens, authorization codes, and client
credentials MUST NOT be transmitted in the clear.The state and scope parameters SHOULD NOT include sensitive
client or resource owner information in plain text, as they can be
transmitted over insecure channels or stored insecurely.Ensuring Endpoint AuthenticityIn order to prevent man-in-the-middle attacks, the authorization
server MUST require the use of TLS with server authentication as
defined by for any request sent to the authorization and
token endpoints. The client MUST validate the authorization server's
TLS certificate as defined by and in accordance with its
requirements for server identity authentication.Credentials-Guessing AttacksThe authorization server MUST prevent attackers from guessing access
tokens, authorization codes, refresh tokens, resource owner
passwords, and client credentials.The probability of an attacker guessing generated tokens (and other
credentials not intended for handling by end-users) MUST be less than
or equal to 2^(-128) and SHOULD be less than or equal to 2^(-160).The authorization server MUST utilize other means to protect
credentials intended for end-user usage.Phishing AttacksWide deployment of this and similar protocols may cause end-users to
become inured to the practice of being redirected to websites where
they are asked to enter their passwords. If end-users are not
careful to verify the authenticity of these websites before entering
their credentials, it will be possible for attackers to exploit this
practice to steal resource owners' passwords.Service providers should attempt to educate end-users about the risks
phishing attacks pose and should provide mechanisms that make it easy
for end-users to confirm the authenticity of their sites. Client
developers should consider the security implications of how they
interact with the user-agent (e.g., external, embedded), and the
ability of the end-user to verify the authenticity of the
authorization server.To reduce the risk of phishing attacks, the authorization servers
MUST require the use of TLS on every endpoint used for end-user
interaction.Fake External User-Agents in Native AppsThe native app that is initiating the authorization request has a
large degree of control over the user interface and can potentially
present a fake external user-agent, that is, an embedded user-agent
made to appear as an external user-agent.When all good actors are using external user-agents, the advantage is
that it is possible for security experts to detect bad actors, as
anyone faking an external user-agent is provably bad. On the other
hand, if good and bad actors alike are using embedded user-agents,
bad actors don't need to fake anything, making them harder to detect.
Once a malicious app is detected, it may be possible to use this
knowledge to blacklist the app's signature in malware scanning
software, take removal action (in the case of apps distributed by app
stores) and other steps to reduce the impact and spread of the
malicious app.Authorization servers can also directly protect against fake external
user-agents by requiring an authentication factor only available to
true external user-agents.Users who are particularly concerned about their security when using
in-app browser tabs may also take the additional step of opening the
request in the full browser from the in-app browser tab and complete
the authorization there, as most implementations of the in-app
browser tab pattern offer such functionality.Malicious External User-Agents in Native AppsIf a malicious app is able to configure itself as the default handler
for https scheme URIs in the operating system, it will be able to
intercept authorization requests that use the default browser and
abuse this position of trust for malicious ends such as phishing the
user.This attack is not confined to OAuth; a malicious app configured in
this way would present a general and ongoing risk to the user beyond
OAuth usage by native apps. Many operating systems mitigate this
issue by requiring an explicit user action to change the default
handler for http and https scheme URIs.Cross-Site Request ForgeryAn attacker might attempt to inject a request to the redirect URI of
the legitimate client on the victim's device, e.g., to cause the
client to access resources under the attacker's control. This is a
variant of an attack known as Cross-Site Request Forgery (CSRF).The traditional countermeasure are CSRF tokens that are bound to the
user agent and passed in the state parameter to the authorization
server as described in . The same protection is provided by
the code_verifier parameter or the OpenID Connect nonce value.When using code_verifier instead of state or nonce for CSRF protection, it is
important to note that:
Clients MUST ensure that the AS supports the code_challenge_method
intended to be used by the client. If an authorization server does not support the requested method,
state or nonce MUST be used for CSRF protection instead.
If state is used for carrying application state, and integrity of
its contents is a concern, clients MUST protect state against
tampering and swapping. This can be achieved by binding the
contents of state to the browser session and/or signed/encrypted
state values .
AS therefore MUST provide a way to detect their supported code challenge methods
either via AS metadata according to or provide a
deployment-specific way to ensure or determine support.ClickjackingAs described in Section 4.4.1.9 of , the authorization
request is susceptible to clickjacking. An attacker can use this
vector to obtain the user's authentication credentials, change the
scope of access granted to the client, and potentially access the
user's resources.Authorization servers MUST prevent clickjacking attacks. Multiple
countermeasures are described in , including the use of the
X-Frame-Options HTTP response header field and frame-busting
JavaScript. In addition to those, authorization servers SHOULD also
use Content Security Policy (CSP) level 2 or greater.To be effective, CSP must be used on the authorization endpoint and,
if applicable, other endpoints used to authenticate the user and
authorize the client (e.g., the device authorization endpoint, login
pages, error pages, etc.). This prevents framing by unauthorized
origins in user agents that support CSP. The client MAY permit being
framed by some other origin than the one used in its redirection
endpoint. For this reason, authorization servers SHOULD allow
administrators to configure allowed origins for particular clients
and/or for clients to register these dynamically.Using CSP allows authorization servers to specify multiple origins in
a single response header field and to constrain these using flexible
patterns (see for details). Level 2 of this standard provides
a robust mechanism for protecting against clickjacking by using
policies that restrict the origin of frames (using frame-ancestors)
together with those that restrict the sources of scripts allowed to
execute on an HTML page (by using script-src). A non-normative
example of such a policy is shown in the following listing:
HTTP/1.1 200 OK
Content-Security-Policy: frame-ancestors https://ext.example.org:8000
Content-Security-Policy: script-src 'self'
X-Frame-Options: ALLOW-FROM https://ext.example.org:8000
...
Because some user agents do not support , this technique
SHOULD be combined with others, including those described in
, unless such legacy user agents are explicitly unsupported
by the authorization server. Even in such cases, additional
countermeasures SHOULD still be employed.Code Injection and Input ValidationA code injection attack occurs when an input or otherwise external
variable is used by an application unsanitized and causes
modification to the application logic. This may allow an attacker to
gain access to the application device or its data, cause denial of
service, or introduce a wide range of malicious side-effects.The authorization server and client MUST sanitize (and validate when
possible) any value received - in particular, the value of the
state and redirect_uri parameters.Open RedirectorsThe following attacks can occur when an AS or client has an open
redirector. An open redirector is an endpoint that forwards a user's
browser to an arbitrary URI obtained from a query parameter.Client as Open RedirectorClients MUST NOT expose open redirectors. Attackers may use open
redirectors to produce URLs pointing to the client and utilize them to
exfiltrate authorization codes and access tokens, as described in
(#redir_uri_open_redir). Another abuse case is to produce URLs that
appear to point to the client. This might trick users into trusting the URL
and follow it in their browser. This can be abused for phishing.In order to prevent open redirection, clients should only redirect if
the target URLs are whitelisted or if the origin and integrity of a
request can be authenticated. Countermeasures against open redirection
are described by OWASP .Authorization Server as Open RedirectorJust as with clients, attackers could try to utilize a user's trust in
the authorization server (and its URL in particular) for performing
phishing attacks. OAuth authorization servers regularly redirect users
to other web sites (the clients), but must do so in a safe way. already prevents open redirects by
stating that the AS MUST NOT automatically redirect the user agent in case
of an invalid combination of client_id and redirect_uri.However, an attacker could also utilize a correctly registered
redirect URI to perform phishing attacks. The attacker could, for
example, register a client via dynamic client registration
and intentionally send an erroneous authorization request, e.g., by
using an invalid scope value, thus instructing the AS to redirect the
user agent to its phishing site.The AS MUST take precautions to prevent this threat. Based on its risk
assessment, the AS needs to decide whether it can trust the redirect
URI and SHOULD only automatically redirect the user agent if it trusts
the redirect URI. If the URI is not trusted, the AS MAY inform the
user and rely on the user to make the correct decision.Authorization Server Mix-Up Mitigation in Native Apps(TODO: merge this with the regular mix-up section when it is brought in)To protect against a compromised or malicious authorization server
attacking another authorization server used by the same app, it is
REQUIRED that a unique redirect URI is used for each authorization
server used by the app (for example, by varying the path component),
and that authorization responses are rejected if the redirect URI
they were received on doesn't match the redirect URI in an outgoing
authorization request.The native app MUST store the redirect URI used in the authorization
request with the authorization session data (i.e., along with state
and other related data) and MUST verify that the URI on which the
authorization response was received exactly matches it.The requirement of , specifically that authorization
servers reject requests with URIs that don't match what was
registered, is also required to prevent such attacks.Embedded User Agents in Native AppsEmbedded user-agents are a technically possible method for authorizing native
apps. These embedded user-agents are unsafe for use by third parties
to the authorization server by definition, as the app that hosts the
embedded user-agent can access the user's full authentication
credential, not just the OAuth authorization grant that was intended
for the app.In typical web-view-based implementations of embedded user-agents,
the host application can record every keystroke entered in the login
form to capture usernames and passwords, automatically submit forms
to bypass user consent, and copy session cookies and use them to
perform authenticated actions as the user.Even when used by trusted apps belonging to the same party as the
authorization server, embedded user-agents violate the principle of
least privilege by having access to more powerful credentials than
they need, potentially increasing the attack surface.Encouraging users to enter credentials in an embedded user-agent
without the usual address bar and visible certificate validation
features that browsers have makes it impossible for the user to know
if they are signing in to the legitimate site; even when they are, it
trains them that it's OK to enter credentials without validating the
site first.Aside from the security concerns, embedded user-agents do not share
the authentication state with other apps or the browser, requiring
the user to log in for every authorization request, which is often
considered an inferior user experience.Other RecommendationsAuthorization servers SHOULD NOT allow clients to influence their
client_id or sub value or any other claim if that can cause
confusion with a genuine resource owner (see (#client_impersonating)).Native ApplicationsNative applications are clients installed and executed on the device
used by the resource owner (i.e., desktop application, native mobile
application). Native applications require special consideration
related to security, platform capabilities, and overall end-user
experience.The authorization endpoint requires interaction between the client
and the resource owner's user-agent. The best current practice is to
perform the OAuth authorization request in an external user-agent
(typically the browser) rather than an embedded user-agent (such as
one implemented with web-views).The native application can capture the
response from the authorization server using a redirect URI
with a scheme registered with the operating system to invoke the
client as the handler, manual copy-and-paste of the credentials,
running a local web server, installing a user-agent extension, or
by providing a redirect URI identifying a server-hosted
resource under the client's control, which in turn makes the
response available to the native application.Previously, it was common for native apps to use embedded user-agents
(commonly implemented with web-views) for OAuth authorization
requests. That approach has many drawbacks, including the host app
being able to copy user credentials and cookies as well as the user
needing to authenticate from scratch in each app. See
for a deeper analysis of the drawbacks of using embedded user-agents
for OAuth.Native app authorization requests that use the browser are more
secure and can take advantage of the user's authentication state.
Being able to use the existing authentication session in the browser
enables single sign-on, as users don't need to authenticate to the
authorization server each time they use a new app (unless required by
the authorization server policy).Supporting authorization flows between a native app and the browser
is possible without changing the OAuth protocol itself, as the OAuth
authorization request and response are already defined in terms of
URIs. This encompasses URIs that can be used for inter-app
communication. Some OAuth server implementations that assume all
clients are confidential web clients will need to add an
understanding of public native app clients and the types of redirect
URIs they use to support this best practice.Using Inter-App URI Communication for OAuth in Native AppsJust as URIs are used for OAuth on the web to initiate
the authorization request and return the authorization response to
the requesting website, URIs can be used by native apps to initiate
the authorization request in the device's browser and return the
response to the requesting native app.By adopting the same methods used on the web for OAuth, benefits seen
in the web context like the usability of a single sign-on session and
the security of a separate authentication context are likewise gained
in the native app context. Reusing the same approach also reduces
the implementation complexity and increases interoperability by
relying on standards-based web flows that are not specific to a
particular platform.Native apps MUST use an external
user-agent to perform OAuth authorization requests. This is achieved
by opening the authorization request in the browser (detailed in
) and using a redirect URI that will return the
authorization response back to the native app (defined in ).Initiating the Authorization Request from a Native AppNative apps needing user authorization create an authorization
request URI with the authorization code grant type per
using a redirect URI capable of being received by the native app.The function of the redirect URI for a native app authorization
request is similar to that of a web-based authorization request.
Rather than returning the authorization response to the OAuth
client's server, the redirect URI used by a native app returns the
response to the app. Several options for a redirect URI that will
return the authorization response to the native app in different
platforms are documented in . Any redirect URI that allows
the app to receive the URI and inspect its parameters is viable.After constructing the authorization request URI, the app uses
platform-specific APIs to open the URI in an external user-agent.
Typically, the external user-agent used is the default browser, that
is, the application configured for handling http and https scheme
URIs on the system; however, different browser selection criteria and
other categories of external user-agents MAY be used.This best practice focuses on the browser as the RECOMMENDED external
user-agent for native apps. An external user-agent designed
specifically for user authorization and capable of processing
authorization requests and responses like a browser MAY also be used.
Other external user-agents, such as a native app provided by the
authorization server may meet the criteria set out in this best
practice, including using the same redirect URI properties, but
their use is out of scope for this specification.Some platforms support a browser feature known as "in-app browser
tabs", where an app can present a tab of the browser within the app
context without switching apps, but still retain key benefits of the
browser such as a shared authentication state and security context.
On platforms where they are supported, it is RECOMMENDED, for
usability reasons, that apps use in-app browser tabs for the
authorization request.Receiving the Authorization Response in a Native AppThere are several redirect URI options available to native apps for
receiving the authorization response from the browser, the
availability and user experience of which varies by platform.To fully support native apps, authorization servers MUST offer
at least the three redirect URI options described in the following
subsections to native apps. Native apps MAY use whichever redirect
option suits their needs best, taking into account platform-specific
implementation details.Private-Use URI Scheme RedirectionMany mobile and desktop computing platforms support inter-app
communication via URIs by allowing apps to register private-use URI
schemes (sometimes colloquially referred to as "custom URL schemes")
like com.example.app. When the browser or another app attempts to
load a URI with a private-use URI scheme, the app that registered it
is launched to handle the request.To perform an authorization request with a private-use URI
scheme redirect, the native app launches the browser with a standard
authorization request, but one where the redirect URI utilizes a
private-use URI scheme it registered with the operating system.When choosing a URI scheme to associate with the app, apps MUST use a
URI scheme based on a domain name under their control, expressed in
reverse order, as recommended by Section 3.8 of for
private-use URI schemes.For example, an app that controls the domain name app.example.com
can use com.example.app as their scheme. Some authorization
servers assign client identifiers based on domain names, for example,
client1234.usercontent.example.net, which can also be used as the
domain name for the scheme when reversed in the same manner. A
scheme such as myapp, however, would not meet this requirement, as
it is not based on a domain name.When there are multiple apps by the same publisher, care must be
taken so that each scheme is unique within that group. On platforms
that use app identifiers based on reverse-order domain names, those
identifiers can be reused as the private-use URI scheme for the OAuth
redirect to help avoid this problem.Following the requirements of Section 3.2 of , as there is
no naming authority for private-use URI scheme redirects, only a
single slash (/) appears after the scheme component. A complete
example of a redirect URI utilizing a private-use URI scheme is:When the authorization server completes the request, it redirects to
the client's redirect URI as it would normally. As the
redirect URI uses a private-use URI scheme, it results in the
operating system launching the native app, passing in the URI as a
launch parameter. Then, the native app uses normal processing for
the authorization response.Claimed "https" Scheme URI RedirectionSome operating systems allow apps to claim https scheme
URIs in the domains they control. When the browser encounters a
claimed URI, instead of the page being loaded in the browser, the
native app is launched with the URI supplied as a launch parameter.Such URIs can be used as redirect URIs by native apps. They are
indistinguishable to the authorization server from a regular web-
based client redirect URI. An example is:As the redirect URI alone is not enough to distinguish public native
app clients from confidential web clients, it is REQUIRED in
that the client type be recorded during client
registration to enable the server to determine the client type and
act accordingly.App-claimed https scheme redirect URIs have some advantages
compared to other native app redirect options in that the identity of
the destination app is guaranteed to the authorization server by the
operating system. For this reason, native apps SHOULD use them over
the other options where possible.Loopback Interface RedirectionNative apps that are able to open a port on the loopback network
interface without needing special permissions (typically, those on
desktop operating systems) can use the loopback interface to receive
the OAuth redirect.Loopback redirect URIs use the http scheme and are constructed with
the loopback IP literal and whatever port the client is listening on.That is, http://127.0.0.1:{port}/{path} for IPv4, and
http://[::1]:{port}/{path} for IPv6. An example redirect using the
IPv4 loopback interface with a randomly assigned port:An example redirect using the IPv6 loopback interface with a randomly
assigned port:The authorization server MUST allow any port to be specified at the
time of the request for loopback IP redirect URIs, to accommodate
clients that obtain an available ephemeral port from the operating
system at the time of the request.Clients SHOULD NOT assume that the device supports a particular
version of the Internet Protocol. It is RECOMMENDED that clients
attempt to bind to the loopback interface using both IPv4 and IPv6
and use whichever is available.Browser-Based AppsBrowser-based apps are are clients that run in a web browser, typically
written in JavaScript, also known as "single-page apps". These types of apps
have particular security considerations similar to native apps.TODO: Bring in the normative text of the browser-based apps BCP when it is finalized.Differences from OAuth 2.0This draft consolidates the functionality in OAuth 2.0 ,
OAuth 2.0 for Native Apps (),
Proof Key for Code Exchange (),
OAuth 2.0 for Browser-Based Apps (),
OAuth Security Best Current Practice (),
and Bearer Token Usage ().Where a later draft updates or obsoletes functionality found in the original
, that functionality in this draft is updated with the normative
changes described in a later draft, or removed entirely.A non-normative list of changes from OAuth 2.0 is listed below:
The authorization code grant is extended with the functionality from PKCE ()
such that the default method of using the authorization code grant according
to this specification requires the addition of the PKCE parameters
Redirect URIs must be compared using exact string matching
as per Section 4.1.3 of
The Implicit grant (response_type=token) is omitted from this specification
as per Section 2.1.2 of
The Resource Owner Password Credentials grant is omitted from this specification
as per Section 2.4 of
Bearer token usage omits the use of bearer tokens in the query string of URIs
as per Section 4.3.2 of
Refresh tokens should either be sender-constrained or one-time use
as per Section 4.12.2 of
IANA ConsiderationsThis document does not require any IANA actions.All referenced registries are defined by RFC6749 and related documents that this
work is based upon. No changes to those registries are required by this specification.ReferencesNormative ReferencesKey words for use in RFCs to Indicate Requirement LevelsIn many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements.HTTP Authentication: Basic and Digest Access AuthenticationThis document provides the specification for HTTP's authentication framework, the original Basic authentication scheme and a scheme based on cryptographic hashes, referred to as "Digest Access Authentication". [STANDARDS-TRACK]HTTP Over TLSThis memo describes how to use Transport Layer Security (TLS) to secure Hypertext Transfer Protocol (HTTP) connections over the Internet. This memo provides information for the Internet community.UTF-8, a transformation format of ISO 10646ISO/IEC 10646-1 defines a large character set called the Universal Character Set (UCS) which encompasses most of the world's writing systems. The originally proposed encodings of the UCS, however, were not compatible with many current applications and protocols, and this has led to the development of UTF-8, the object of this memo. UTF-8 has the characteristic of preserving the full US-ASCII range, providing compatibility with file systems, parsers and other software that rely on US-ASCII values but are transparent to other values. This memo obsoletes and replaces RFC 2279.Uniform Resource Identifier (URI): Generic SyntaxA Uniform Resource Identifier (URI) is a compact sequence of characters that identifies an abstract or physical resource. This specification defines the generic URI syntax and a process for resolving URI references that might be in relative form, along with guidelines and security considerations for the use of URIs on the Internet. The URI syntax defines a grammar that is a superset of all valid URIs, allowing an implementation to parse the common components of a URI reference without knowing the scheme-specific requirements of every possible identifier. This specification does not define a generative grammar for URIs; that task is performed by the individual specifications of each URI scheme. [STANDARDS-TRACK]Internet Security Glossary, Version 2This Glossary provides definitions, abbreviations, and explanations of terminology for information system security. The 334 pages of entries offer recommendations to improve the comprehensibility of written material that is generated in the Internet Standards Process (RFC 2026). The recommendations follow the principles that such writing should (a) use the same term or definition whenever the same concept is mentioned; (b) use terms in their plainest, dictionary sense; (c) use terms that are already well-established in open publications; and (d) avoid terms that either favor a particular vendor or favor a particular technology or mechanism over other, competing techniques that already exist or could be developed. This memo provides information for the Internet community.Augmented BNF for Syntax Specifications: ABNFInternet technical specifications often need to define a formal syntax. Over the years, a modified version of Backus-Naur Form (BNF), called Augmented BNF (ABNF), has been popular among many Internet specifications. The current specification documents ABNF. It balances compactness and simplicity with reasonable representational power. The differences between standard BNF and ABNF involve naming rules, repetition, alternatives, order-independence, and value ranges. This specification also supplies additional rule definitions and encoding for a core lexical analyzer of the type common to several Internet specifications. [STANDARDS-TRACK]Representation and Verification of Domain-Based Application Service Identity within Internet Public Key Infrastructure Using X.509 (PKIX) Certificates in the Context of Transport Layer Security (TLS)Many application technologies enable secure communication between two entities by means of Internet Public Key Infrastructure Using X.509 (PKIX) certificates in the context of Transport Layer Security (TLS). This document specifies procedures for representing and verifying the identity of application services in such interactions. [STANDARDS-TRACK]The OAuth 2.0 Authorization FrameworkThe OAuth 2.0 authorization framework enables a third-party application to obtain limited access to an HTTP service, either on behalf of a resource owner by orchestrating an approval interaction between the resource owner and the HTTP service, or by allowing the third-party application to obtain access on its own behalf. This specification replaces and obsoletes the OAuth 1.0 protocol described in RFC 5849. [STANDARDS-TRACK]The OAuth 2.0 Authorization Framework: Bearer Token UsageThis specification describes how to use bearer tokens in HTTP requests to access OAuth 2.0 protected resources. Any party in possession of a bearer token (a "bearer") can use it to get access to the associated resources (without demonstrating possession of a cryptographic key). To prevent misuse, bearer tokens need to be protected from disclosure in storage and in transport. [STANDARDS-TRACK]Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) ProfileThis memo profiles the X.509 v3 certificate and X.509 v2 certificate revocation list (CRL) for use in the Internet. An overview of this approach and model is provided as an introduction. The X.509 v3 certificate format is described in detail, with additional information regarding the format and semantics of Internet name forms. Standard certificate extensions are described and two Internet-specific extensions are defined. A set of required certificate extensions is specified. The X.509 v2 CRL format is described in detail along with standard and Internet-specific extensions. An algorithm for X.509 certification path validation is described. An ASN.1 module and examples are provided in the appendices. [STANDARDS-TRACK]The JavaScript Object Notation (JSON) Data Interchange FormatJavaScript Object Notation (JSON) is a lightweight, text-based, language-independent data interchange format. It was derived from the ECMAScript Programming Language Standard. JSON defines a small set of formatting rules for the portable representation of structured data.This document removes inconsistencies with other specifications of JSON, repairs specification errors, and offers experience-based interoperability guidance.Hypertext Transfer Protocol (HTTP/1.1): Semantics and ContentThe Hypertext Transfer Protocol (HTTP) is a stateless \%application- level protocol for distributed, collaborative, hypertext information systems. This document defines the semantics of HTTP/1.1 messages, as expressed by request methods, request header fields, response status codes, and response header fields, along with the payload of messages (metadata and body content) and mechanisms for content negotiation.Hypertext Transfer Protocol (HTTP/1.1): CachingThe Hypertext Transfer Protocol (HTTP) is a stateless \%application- level protocol for distributed, collaborative, hypertext information systems. This document defines HTTP caches and the associated header fields that control cache behavior or indicate cacheable response messages.Guidelines and Registration Procedures for URI SchemesThis document updates the guidelines and recommendations, as well as the IANA registration processes, for the definition of Uniform Resource Identifier (URI) schemes. It obsoletes RFC 4395.Ambiguity of Uppercase vs Lowercase in RFC 2119 Key WordsRFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings.OAuth 2.0 for Native AppsOAuth 2.0 authorization requests from native apps should only be made through external user-agents, primarily the user's browser. This specification details the security and usability reasons why this is the case and how native apps and authorization servers can implement this best practice.The JavaScript Object Notation (JSON) Data Interchange FormatJavaScript Object Notation (JSON) is a lightweight, text-based, language-independent data interchange format. It was derived from the ECMAScript Programming Language Standard. JSON defines a small set of formatting rules for the portable representation of structured data.This document removes inconsistencies with other specifications of JSON, repairs specification errors, and offers experience-based interoperability guidance.OAuth 2.0 Security Best Current PracticeThis document describes best current security practice for OAuth 2.0. It updates and extends the OAuth 2.0 Security Threat Model to incorporate practical experiences gathered since OAuth 2.0 was published and covers new threats relevant due to the broader application of OAuth 2.0.Recommendations for Secure Use of Transport Layer Security (TLS)n.d.Coded Character Set -- 7-bit American Standard Code for Information Interchange, ANSI X3.4HTML 4.01 SpecificationExtensible Markup Language (XML) 1.0 (Fifth Edition)Informative ReferencesHTTP State Management MechanismThis document defines the HTTP Cookie and Set-Cookie header fields. These header fields can be used by HTTP servers to store state (called cookies) at HTTP user agents, letting the servers maintain a stateful session over the mostly stateless HTTP protocol. Although cookies have many historical infelicities that degrade their security and privacy, the Cookie and Set-Cookie header fields are widely used on the Internet. This document obsoletes RFC 2965. [STANDARDS-TRACK]OAuth 2.0 Threat Model and Security ConsiderationsThis document gives additional security considerations for OAuth, beyond those in the OAuth 2.0 specification, based on a comprehensive threat model for the OAuth 2.0 protocol. This document is not an Internet Standards Track specification; it is published for informational purposes.OAuth 2.0 Token RevocationThis document proposes an additional endpoint for OAuth authorization servers, which allows clients to notify the authorization server that a previously obtained refresh or access token is no longer needed. This allows the authorization server to clean up security credentials. A revocation request will invalidate the actual token and, if applicable, other tokens based on the same authorization grant.Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and RoutingThe Hypertext Transfer Protocol (HTTP) is a stateless application-level protocol for distributed, collaborative, hypertext information systems. This document provides an overview of HTTP architecture and its associated terminology, defines the "http" and "https" Uniform Resource Identifier (URI) schemes, defines the HTTP/1.1 message syntax and parsing requirements, and describes related security concerns for implementations.Hypertext Transfer Protocol (HTTP/1.1): AuthenticationThe Hypertext Transfer Protocol (HTTP) is a stateless application- level protocol for distributed, collaborative, hypermedia information systems. This document defines the HTTP Authentication framework.JSON Web Token (JWT)JSON Web Token (JWT) is a compact, URL-safe means of representing claims to be transferred between two parties. The claims in a JWT are encoded as a JSON object that is used as the payload of a JSON Web Signature (JWS) structure or as the plaintext of a JSON Web Encryption (JWE) structure, enabling the claims to be digitally signed or integrity protected with a Message Authentication Code (MAC) and/or encrypted.OAuth 2.0 Dynamic Client Registration ProtocolThis specification defines mechanisms for dynamically registering OAuth 2.0 clients with authorization servers. Registration requests send a set of desired client metadata values to the authorization server. The resulting registration responses return a client identifier to use at the authorization server and the client metadata values registered for the client. The client can then use this registration information to communicate with the authorization server using the OAuth 2.0 protocol. This specification also defines a set of common client metadata fields and values for clients to use during registration.OAuth 2.0 Dynamic Client Registration Management ProtocolThis specification defines methods for management of OAuth 2.0 dynamic client registrations for use cases in which the properties of a registered client may need to be changed during the lifetime of the client. Not all authorization servers supporting dynamic client registration will support these management methods.Proof Key for Code Exchange by OAuth Public ClientsOAuth 2.0 public clients utilizing the Authorization Code Grant are susceptible to the authorization code interception attack. This specification describes the attack as well as a technique to mitigate against the threat through the use of Proof Key for Code Exchange (PKCE, pronounced "pixy").OAuth 2.0 Token IntrospectionThis specification defines a method for a protected resource to query an OAuth 2.0 authorization server to determine the active state of an OAuth 2.0 token and to determine meta-information about this token. OAuth 2.0 deployments can use this method to convey information about the authorization context of the token from the authorization server to the protected resource.OAuth 2.0 Authorization Server MetadataThis specification defines a metadata format that an OAuth 2.0 client can use to obtain the information needed to interact with an OAuth 2.0 authorization server, including its endpoint locations and authorization server capabilities.OAuth 2.0 Device Authorization GrantThe OAuth 2.0 device authorization grant is designed for Internet- connected devices that either lack a browser to perform a user-agent- based authorization or are input constrained to the extent that requiring the user to input text in order to authenticate during the authorization flow is impractical. It enables OAuth clients on such devices (like smart TVs, media consoles, digital picture frames, and printers) to obtain user authorization to access protected resources by using a user agent on a separate device.OAuth 2.0 Mutual-TLS Client Authentication and Certificate-Bound Access TokensThis document describes OAuth client authentication and certificate-bound access and refresh tokens using mutual Transport Layer Security (TLS) authentication with X.509 certificates. OAuth clients are provided a mechanism for authentication to the authorization server using mutual TLS, based on either self-signed certificates or public key infrastructure (PKI). OAuth authorization servers are provided a mechanism for binding access tokens to a client's mutual-TLS certificate, and OAuth protected resources are provided a method for ensuring that such an access token presented to it was issued to the client presenting the token.Resource Indicators for OAuth 2.0This document specifies an extension to the OAuth 2.0 Authorization Framework defining request parameters that enable a client to explicitly signal to an authorization server about the identity of the protected resource(s) to which it is requesting access.JSON Web Token (JWT) Profile for OAuth 2.0 Access TokensThis specification defines a profile for issuing OAuth 2.0 access tokens in JSON web token (JWT) format. Authorization servers and resource servers from different vendors can leverage this profile to issue and consume access tokens in interoperable manner.OAuth 2.0 Rich Authorization RequestsThis document specifies a new parameter "authorization_details" that is used to carry fine grained authorization data in the OAuth authorization request.OAuth 2.0 Pushed Authorization RequestsThis document defines the pushed authorization request endpoint, which allows clients to push the payload of an OAuth 2.0 authorization request to the authorization server via a direct request and provides them with a request URI that is used as reference to the data in a subsequent call to the authorization endpoint.Encoding claims in the OAuth 2 state parameter using a JWTThis draft provides a method for a client to encode one or more elements encoding information about the session into the OAuth 2 "state" parameter.OAuth 2.0 Token BindingThis specification enables OAuth 2.0 implementations to apply Token Binding to Access Tokens, Authorization Codes, Refresh Tokens, JWT Authorization Grants, and JWT Client Authentication. This cryptographically binds these tokens to a client's Token Binding key pair, possession of which is proven on the TLS connections over which the tokens are intended to be used. This use of Token Binding protects these tokens from man-in-the-middle and token export and replay attacks.OAuth 2.0 for Browser-Based AppsThis specification details the security considerations and best practices that must be taken into account when developing browser- based applications that use OAuth 2.0.OAuth 2.0 Demonstrating Proof-of-Possession at the Application Layer (DPoP)This document describes a mechanism for sender-constraining OAuth 2.0 tokens via a proof-of-possession mechanism on the application level. This mechanism allows for the detection of replay attacks with access and refresh tokens.OpenID Connect Core 1.0Online Multimedia Authorization Protocol: An Industry Standard for Authorized Access to Internet Multimedia ResourcesNIST Special Publication 800-63-1, INFORMATION SECURITYOpenID Connect Messages 1.0OWASP Cheat Sheet Series - Unvalidated Redirects and ForwardsContent Security Policy Level 2Augmented Backus-Naur Form (ABNF) SyntaxThis section provides Augmented Backus-Naur Form (ABNF) syntax
descriptions for the elements defined in this specification using the
notation of . The ABNF below is defined in terms of Unicode
code points ; these characters are typically
encoded in UTF-8. Elements are presented in the order first defined.Some of the definitions that follow use the "URI-reference"
definition from .Some of the definitions that follow use these common definitions:(The UNICODECHARNOCRLF definition is based upon the Char definition
in Section 2.2 of , but omitting the Carriage
Return and Linefeed characters.)"client_id" SyntaxThe client_id element is defined in :"client_secret" SyntaxThe client_secret element is defined in :"response_type" SyntaxThe response_type element is defined in and :"scope" SyntaxThe scope element is defined in :"state" SyntaxThe state element is defined in , , and :"redirect_uri" SyntaxThe redirect_uri element is defined in , and :"error" SyntaxThe error element is defined in Sections , ,
7.2, and 8.5:"error_description" SyntaxThe error_description element is defined in Sections ,
, and :"error_uri" SyntaxThe error_uri element is defined in Sections , ,
and 7.2:"grant_type" SyntaxThe grant_type element is defined in Sections , , ,
, and :"code" SyntaxThe code element is defined in :"access_token" SyntaxThe access_token element is defined in and :"token_type" SyntaxThe token_type element is defined in , and :"expires_in" SyntaxThe expires_in element is defined in :"refresh_token" SyntaxThe refresh_token element is defined in and :Endpoint Parameter SyntaxThe syntax for new endpoint parameters is defined in :"code_verifier" SyntaxABNF for code_verifier is as follows."code_challenge" SyntaxABNF for code_challenge is as follows.Use of application/x-www-form-urlencoded Media TypeAt the time of publication of this specification, the
application/x-www-form-urlencoded media type was defined in
Section 17.13.4 of but not registered in
the IANA MIME Media Types registry
(http://www.iana.org/assignments/media-types). Furthermore, that
definition is incomplete, as it does not consider non-US-ASCII
characters.To address this shortcoming when generating payloads using this media
type, names and values MUST be encoded using the UTF-8 character
encoding scheme first; the resulting octet sequence then
needs to be further encoded using the escaping rules defined in
.When parsing data from a payload using this media type, the names and
values resulting from reversing the name/value encoding consequently
need to be treated as octet sequences, to be decoded using the UTF-8
character encoding scheme.For example, the value consisting of the six Unicode code points
(1) U+0020 (SPACE), (2) U+0025 (PERCENT SIGN),
(3) U+0026 (AMPERSAND), (4) U+002B (PLUS SIGN),
(5) U+00A3 (POUND SIGN), and (6) U+20AC (EURO SIGN) would be encoded
into the octet sequence below (using hexadecimal notation):and then represented in the payload as:ExtensionsBelow is a list of well-established extensions at the time of publication:
: OAuth 2.0 Device Authorization Grant
The Device Authorization Grant (formerly known as the Device Flow) is an extension that enables devices with no browser or limited input capability to obtain an access token. This is commonly used by smart TV apps, or devices like hardware video encoders that can stream video to a streaming video service.
: Authorization Server Metadata
Authorization Server Metadata (also known as OAuth Discovery) defines an endpoint clients can use to look up the information needed to interact with a particular OAuth server, such as the location of the authorization and token endpoints and the supported grant types.
: Resource Indicators
Provides a way for the client to explicitly signal to the authorization server where it intends to use the access token it is requesting.
: Dynamic Client Registration
Dynamic Client Registration provides a mechanism for programmatically registering clients with an authorization server.
: Dynamic Client Management
Dynamic Client Management provides a mechanism for updating dynamically registered client information.
: JSON Web Token (JWT) Profile for OAuth 2.0 Access Tokens
This specification defines a profile for issuing OAuth access tokens in JSON Web Token (JWT) format.
: Mutual TLS
Mutual TLS describes a mechanism of binding access tokens and refresh tokens to the clients they were issued to, as well as a client authentication mechanism, via TLS certificate authentication.
: Token Introspection
The Token Introspection extension defines a mechanism for resource servers to obtain information about access tokens.
: Token Revocation
The Token Revocation extension defines a mechanism for clients to indicate to the authorization server that an access token is no longer needed.
: Pushed Authorization Requests
The Pushed Authorization Requsts extension describes a technique of initiating an OAuth flow from the back channel, providing better security and more flexibility for building complex authorization requests.
: Rich Authorization Requests
Rich Authorization Requests specifies a new parameter authorization_details that is used to carry fine-grained authorization data in the OAuth authorization request.