wdiff draft-ietf-oauth-v2-11.txt draft-ietf-oauth-v2-12.txt

Network Working Group E. Hammer-Lahav, Ed.
Internet-Draft Yahoo!
Obsoletes: 5849 (if approved) D. Recordon
Intended status: Standards Track Facebook
Expires: June 4, July 25, 2011 D. Hardt
Microsoft
December 1, 2010
January 21, 2011

The OAuth 2.0 Authorization Protocol Framework
draft-ietf-oauth-v2-11
draft-ietf-oauth-v2-12

Abstract

This specification describes the OAuth 2.0 protocol framework. authorization protocol.

Status of this Memo

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Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 3
1.1. Notational Conventions . . . Roles . . . . . . . . . . . . . . . 5
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 5
1.3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . 7
1.4. 3
1.2. Access Grants . . . . . . . . . . . . . . . . . . . . . . 8
1.4.1. Authorization Code . . . Token . . . . . . . . . . . . . . . 8
1.4.2. Resource Owner Password Credentials . . . . . . . . 5
1.3. Authorization Grant . 10
1.4.3. Client Credentials . . . . . . . . . . . . . . . . . . 10
1.4.4. 6
1.4. Refresh Token . . . . . . . . . . . . . . . . . . . . 11
1.4.5. Assertion . . . . 7
1.5. Notational Conventions . . . . . . . . . . . . . . . . . . 12 9
2. Client Profiles . Authentication . . . . . . . . . . . . . . . . . . . . . . 12 9
2.1. Web Server . . . . . . . . . . Client Password Authentication . . . . . . . . . . . . . . 12 9
2.2. User-Agent . . . . . . . . . . . . . . . . . . . . . . . . 14
2.3. Native Application . . . . . . . . . . . . . . . . . . . . 15
2.4. Autonomous . . . . . . . . . . . . . Other Client Authentication Methods . . . . . . . . . . . 16 10
3. Client Credentials Protocol Endpoints . . . . . . . . . . . . . . . . . . . . . . 17 11
3.1. Client Password Credentials . . . . . . . . . . . . . . . 17
3.2. Client Assertion Credentials . . . . . . . . . . . . . . . 18
4. Obtaining End-User Authorization Endpoint . . . . . . . . . . . . . . . 20
4.1. Authorization Request . . . . . . . . . . . . . . . . . . 20
4.2. Authorization Response . . . . 11
3.2. Token Endpoint . . . . . . . . . . . . . . 22
4.3. Error Response . . . . . . . . . . . 12
4. Requesting an Access Token . . . . . . . . . . . 24
4.3.1. Error Codes . . . . . . . 13
4.1. Authorization Code . . . . . . . . . . . . . . 25
5. Obtaining an Access Token . . . . . . 13
4.2. Implicit Grant . . . . . . . . . . . . 25
5.1. Access Grant Types . . . . . . . . . . 19
4.3. Resource Owner Password Credentials . . . . . . . . . . 27
5.1.1. Authorization Code . 24
4.4. Client Credentials . . . . . . . . . . . . . . . . . 27
5.1.2. Resource Owner Password Credentials . . . 26
4.5. Extensions . . . . . . 27
5.1.3. Client Credentials . . . . . . . . . . . . . . . . . . 28
5.1.4. Refresh
5. Issuing an Access Token . . . . . . . . . . . . . . . . . . . . 28
5.1.5. Assertion . . .
5.1. Successful Response . . . . . . . . . . . . . . . . . . . 29 28
5.2. Access Token Response . . . . . . . . . . . . . . . . . . 30
5.3. Error Response . . . . . . . . . . . . . . . . . . . . . . 31
5.3.1. Error Codes . . . 30
6. Refreshing an Access Token . . . . . . . . . . . . . . . . . . 32
6. 31
7. Accessing a Protected Resource Resources . . . . . . . . . . . . . . . . 33
6.1. 32
7.1. Access Token Types . . . . . . . . . . . . . . . . . . . . 33
6.2. The WWW-Authenticate Response Header Field . . . . . . . . 33
6.2.1. Error Codes . . . . . . . . . . . . . . . . . . . . . 35
7.
8. Extensibility . . . . . . . . . . . . . . . . . . . . . . . . 36
7.1. 33
8.1. Defining New Client Credentials Access Token Types . . . . . . . . . . 36
7.2. Defining New Endpoint Parameters . . . . . . . . . . . . . 36
7.3. 33
8.2. Defining New Header Field Endpoint Parameters . . . . . . . . . . . 36
7.4. . . 34
8.3. Defining New Access Authorization Grant Types . . . . . . . . . . . . . 37
8. 34
9. Security Considerations . . . . . . . . . . . . . . . . . . . 37
9. 34
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 37
9.1. 35
10.1. The OAuth Parameters Access Token Type Registry . . . . . . . . . . . . . . 37
9.1.1. Registration Template . . . . . . . . . . . . . . . . 37
9.1.2. Example . . . . . . . . . 35
10.2. The OAuth Parameters Registry . . . . . . . . . . . . . . 38 36
Appendix A. Examples . . . . . . . . . . . . . . . . . . . . . . 38 39
Appendix B. Contributors . . . . . . . . . . . . . . . . . . . . 38 39
Appendix C. Acknowledgements . . . . . . . . . . . . . . . . . . 39
Appendix D. Document History . . . . . . . . . . . . . . . . . . 39
10.
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 44
10.1. 43
11.1. Normative References . . . . . . . . . . . . . . . . . . . 44
10.2. 43
11.2. Informative References . . . . . . . . . . . . . . . . . . 45
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 46 45

1. Introduction

With the increasing use of distributed web services and cloud
computing, third-party applications require access to server-hosted
resources. These resources are usually protected and require
authentication using the resource owner's credentials (typically a
username and password).

In the traditional client-server authentication model, the client
accesses a 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 protected resources, the
resource owner shares its credentials with the third-party. This
creates several problems and limitations:

o Third-party applications are required to store the resource-
owner's credentials for future use, typically a password in clear-
text.
o Servers are required to support password authentication, despite
the security weaknesses created by passwords.
o 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, to
limit access duration, or to limit access to the methods supported
by these
resources.
o Resource owners cannot revoke access to an individual third-party
without revoking access to all third-parties, and must do so by
changing their 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 (which is
usually not the resource owner, but is acting on the resource owner's
behalf) requests access to resources controlled
by the resource owner and hosted by the resource server, and is
issued a different set of credentials than those of the resource
owner.

Instead of using the resource owner's credentials to access protected
resources, the client obtains an access token - a string which
denotes denoting a
specific scope, duration, and other access attributes. Access tokens
are issued to third-party 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, a web user (resource owner) can grant a printing service
(client) access to her protected photos stored at a photo sharing
service (resource server), without sharing her username and password
with the printing service. Instead, she authenticates directly with
an authentication service
a server trusted by the photo sharing service (authorization server)
which issues the printing service delegation-
specific delegation-specific credentials (token).

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 are beyond the scope of
this specification and are defined by companion specifications. The
interaction between the authorization server and resource server is
beyond the scope of this specification.
(access token).

1.1. Notational Conventions

The key words 'MUST', 'MUST NOT', 'REQUIRED', 'SHALL', 'SHALL NOT',
'SHOULD', 'SHOULD NOT', 'RECOMMENDED', 'MAY', and 'OPTIONAL' in this
document are Roles

OAuth includes four roles working together to be interpreted as described in [RFC2119].

This document uses the Augmented Backus-Naur Form (ABNF) notation of
[I-D.ietf-httpbis-p1-messaging]. Additionally, the following rules
are included from [RFC3986]: URI-reference; and from
[I-D.ietf-httpbis-p1-messaging]: OWS, RWS, and quoted-string.

Unless otherwise noted, all the protocol parameter names grant and values
are case sensitive.

1.2. Terminology provide
access to protected resource
An access-restricted resource resources - access restricted resources which can be obtained using an
OAuth-authenticated request.

resource server
A server capable of accepting and responding
require authentication to protected
resource requests.

client
An application obtaining authorization and making protected
resource requests. access:

resource owner
An entity capable of granting access to a protected resource.

end-user
A human resource owner.

token
A string representing an access authorization issued to
When the
client. The string resource owner is usually opaque a person, it is referred to the client. Tokens
represent specific scopes and durations of access, granted by
the resource owner, and enforced by the as an end-
user.
resource server and
authorization servers.
The token may denote an identifier used
to retrieve the authorization information, or self-contain server hosting the
authorization information in a verifiable manner (i.e. a token
string consisting protected resources, capable of some data accepting
and a signature). Tokens may be
pure capabilities. Specific additional authentication
credentials may be required in order for a client responding to use a
token. protected resource requests using access token
A token used by the tokens.
client to make authenticated
An application making protected resource requests on behalf of the
resource owner.

refresh token
A token used by the client to obtain a new access token without
having to involve the resource owner.

authorization code A short-lived token representing the
authorization provided by the end-user. The authorization code
is used to obtain an access token and a refresh token.

access grant A general term used to describe the intermediate
credentials (such as an end-user password or authorization
code) representing the resource owner and with its authorization. Access
grants are used by the client to obtain an access token. By
exchanging access grants of different types for an access
token, the resource server is only required to support a single
authentication scheme.
authorization server
A
The server capable of issuing access tokens to the client after successfully
authenticating the resource owner and obtaining authorization.

The interaction between the authorization server and resource server
is beyond the scope of this specification. The authorization server
may be the same server as the resource
server, server or a separate entity.
A single authorization server may issue access tokens for accepted by
multiple resource servers.

end-user authorization endpoint
The authorization server's HTTP endpoint capable of
authenticating

When interacting with the end-user and obtaining authorization. The
end-user authorization endpoint is described in Section 4.

token endpoint
The authorization server's HTTP endpoint capable of issuing
tokens and refreshing expired tokens. The token endpoint is
described in Section 5.

client identifier
A unique identifier issued to server, the client to identify identifies
itself to
the authorization server. Client identifiers may have a
matching secret. The client identifier is described in
Section 3.

1.3. Overview

OAuth provides a method for clients to access using a protected resource on
behalf set of a resource owner. Before a client can access credentials which include a protected
resource, it must first obtain authorization (access grant) from the
resource owner, then exchange the access grant for an access token
(representing the grant's scope, duration, client
identifier and other attributes). authentication attributes. The client accesses means through
which the protected resource by presenting client obtains its credentials are beyond the access
token to scope of this
specification, but typically involve registration with the resource server.

The access token provides an abstraction layer, replacing different
authorization constructs (e.g. username and password, assertion) for
a single token understood by the resource server. This abstraction
enables issuing access tokens valid for a short time period, as well
as removing the resource server's need to understand a wide range of
authentication schemes.

+--------+ +---------------+
| |--(A)- Authorization Request ->| Resource |
| | | Owner |
| |<-(B)----- Access |<-(B)-- Authorization Grant -------| ---| |
| | +---------------+
| |
| | Access Authorization Grant & +---------------+
| |--(C)--- Client Credentials -->| Authorization |
| Client | | Server |
| |<-(D)----- Access Token -------| |
| | +---------------+
| |
| | +---------------+
| |--(E)----- Access Token ------>| Resource |
| | | Server |
| |<-(F)--- Protected Resource ---| |
+--------+ +---------------+
Figure 1: Abstract Protocol Flow

The abstract flow illustrated in Figure 1 describes the overall
protocol architecture interaction
between the four roles and includes the following steps:

(A) The client requests authorization from the resource owner. The
authorization request can be made directly to the resource
owner, owner
(as shown), or preferably indirectly via an intermediary such as
an authorization server.
(B) The client receives an access authorization grant which represents the
authorization provided by the resource owner. The authorization
grant type depends on the method used by the client and
supported by the authorization server to obtain it.
(C) The client requests an access token by authenticating with the
authorization server using its client credentials, credentials (prearranged
between the client and authorization server) and presenting the access
authorization grant.
(D) The authorization server validates the client credentials and
the access authorization grant, and if valid issues an access token.
(E) The client makes a requests the protected resource request to from the resource
server and authenticates by presenting the access token.
(F) The resource server validates the access token, and if valid,
serves the request.

1.4.

1.2. Access Grants

The Token

An access grant represents the token is a string representing an authorization provided issued to
the client. The string is usually opaque to the client. Tokens
represent specific scopes and durations of access, granted by the
resource owner. owner, and enforced by the resource server and authorization
server.

The token may denote an identifier used to retrieve the authorization
information, or self-contain the authorization information in a
verifiable manner (i.e. a token string consisting of some data and a
signature). Tokens may be pure capabilities. Additional
authentication credentials may be required in order for the client to
use a token.

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 type depends
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 method resource
server security requirements. Access token attributes and the
methods used by to access protected resources are beyond the client scope of
this specification and supported are defined by companion specifications.

1.3. Authorization Grant

An authorization grant is a general term used to describe the
intermediate credentials representing the resource owner
authorization, and serves as an abstraction layer. An authorization server
grant is used by the client to obtain it.

1.4.1. an access token.

1.3.1. Authorization Code

The authorization code is an access grant obtained by directing the
end-user to using an authorization server. The authorization server
authenticates
as an intermediary between the end-user, obtains authorization, client and issues resource owner. Instead of
requesting authorization directly from the resource owner, the client
directs the resource owner to an authorization code server (via its user-
agent), which in turns directs the resource owner back to the client. client
with the authorization code.

Before directing the resource owner back to the client with the
authorization code, the authorization server authenticates the
resource owner and obtains authorization. Because the end-user resource owner
only authenticates with the authorization server, the end-user's password
is resource
owner's credentials are never shared with the client.

The authorization code access grant is suitable when the client is
interacting with an end-user via provides a user-agent.

+----------+
| |
| End-User |
| |
+----------+
^
|
(B)
+----|-----+ Client Identifier +---------------+
| -+--(A)--- & Redirect URI ----->| |
| User- | | Authorization |
| Agent -|--(B)-- User authenticates -->| Server |
| | | |
| -+--(C)-- Authorization Code --<| |
+-|----|---+ +---------------+
(A) (C)
| |
^ v
+---------+
| |
| Client |
| |
+---------+

Figure 2: Obtaining an Authorization Code

The authorization code flow illustrated in Figure 2 includes the
following steps:

(A) The client initiates the flow by directing few important security benefits
such as the end-user's user-
agent ability to authenticate the authorization server's end-user authorization
endpoint. The client includes its client identifier, requested
scope, local state, and a redirection URI (to which the
authorization server will send issuing the user-agent back once access
is granted or denied).

(B) The authorization server authenticates the end-user (via the
user-agent) and establishes whether
token directly to the end-user grants or
denies client without potentially exposing it to
others, including the client's access request.

1.3.2. Implicit

An implicit grant is granted, issued when the resource owner's authorization server directs the user-
agent back to the client
is expressed directly as an access token, without using the redirection URI provided. an
intermediate credential. The authorization server includes implicit grant is issued in a similar
manner as an authorization code for code, but instead of the
client to use resource owner
being redirected back to obtain an access token.

Once the client obtains an with the authorization code, it requests
is redirected back with an access token by authenticating with and its related attributes.

When issuing an implicit grant, the authorization server (using its
client credentials) cannot
verify the identity of the client, and presenting the authorization code (access
grant).

In cases where access token may be
exposed to the client is incapable resource owner or other applications with access to
the resource owner's user-agent.

Implicit grants improve the responsiveness and efficiency of maintaining its client
credentials secret some
clients (such as native applications or an application a client implemented as a user-agent script), the authorization server issues an access token directly to in-browser application)
since it reduces the client in step (C), instead number of
issuing an authorization code.

Obtaining round trip required to obtain an authorization code is described in Section 4.

1.4.2.
access token.

1.3.3. Resource Owner Password Credentials

The resource owner password credentials (e.g. a username and
password) can be used directly as an access authorization grant to obtain an
access token. The credentials should only be used when there is a
high degree of trust between the resource owner and the client (e.g.
its computer operating system or a highly privileged application),
and when other access authorization grant types are not available (such as
an authorization code).

Even though this grant type requires direct client access to the
resource owner's owner credentials, the resource owner's owner credentials are used
for a single request and are exchanged for an access token. Unlike
the HTTP Basic authentication scheme defined in [RFC2617], this grant
type eliminates the need for the client to store the
resource-owner's resource-owner
credentials for future use.

In Figure 3, the client requests authorization from the resource
owner directly. When the resource owner is an end-user, the client
typically prompts the end-user for the username and password.

+--------+ +----------+
| |--(A)- Authorization Request ->| Resource |
| Client | | Owner |
| |<-(B)-- Username & Password ---| |
+--------+ +----------+

Figure 3: Obtaining Resource Owner Password Credentials

1.4.3.

1.3.4. Client Credentials

The client credentials can be used as an access authorization grant when the
authorization scope is limited to the protected resources under the
control of the client, or other to protected resources previously arranged
with the authorization server. Client credentials are used as an access
authorization grant typically when the client is acting on its own
behalf (the client is also the resource owner).

1.4.4. Refresh Token

Access tokens usually have

1.3.5. Extensions

Additional grant types may be defined to provide a shorter lifetime than authorized by the
resource owner. When issuing bridge between
OAuth and other trust frameworks. For example,
[I-D.ietf-oauth-saml2-bearer] defines a SAML 2.0
[OASIS.saml-core-2.0-os] bearer assertion grant type, which can be
used to obtain an access token, the authorization
server can include a token.

1.4. Refresh Token

A refresh token which is used optionally issued by the client authorization server to
obtain a new access token when
the current access token expires.
When requesting a new client together with an access token, token. The client can use the
refresh token acts as an to request another access grant. Using a refresh token removes based on the need same
authorization, without having to interact
with involve the resource owner again, or
having to store retain the original access authorization grant used to obtain the
initial access token.

A refresh token and is a string representing the authorization granted to
the client by the resource owner. The string is usually opaque to
the client. The token may denote an identifier used to retrieve the
authorization information, or self-contain the authorization
information in a verifiable manner.

The refresh token. token can be used to obtain a new access token when the
current access token expires (access tokens may have a shorter
lifetime than authorized by the resource owner), or to obtain
additional access tokens with identical or narrower scope.

+--------+ Access Grant & +---------------+
| |--(A)-- |--(A)-------- Client Credentials -->| Authorization --------->| |
| | | Server |
| |<-(B)---- |<-(B)----------- Access Token -------| -------------| |
| | & Refresh Token +---------------+ | |
| | +---------------+ | |--(C)----- |
| | +----------+ | |
| |--(C)---- Access Token ----->| ---->| | | |
| | | | |<-(D)-- | |
| |<-(D)- Protected Resource ---| --| Resource | | Authorization |
| Client | | Server | | |--(E)----- Server |
| |--(E)---- Access Token ----->| ---->| | | |
| | | | | |
| |<-(F)-- |<-(F)- Invalid Token Error --| -| | | |
| | +----------+ | |
| | +---------------+ | |
| | Refresh Token & +---------------+ | |--(G)-- |
| |--(G)-------- Client Credentials -->| Authorization --------->| |
| | | Server |
| |<-(H)----- |<-(H)----------- Access Token ------| -------------| |
+--------+ & Optional Refresh Token +---------------+

Figure 4: 2: Refreshing an Expired Access Token

The refresh token flow illustrated in Figure 4 2 includes the following steps:

(A) The client requests an access token by authenticating with the
authorization server using its client credentials, and
presenting an access authorization grant.
(B) The authorization server validates the client credentials and
the access authorization grant, and if valid issues an access token and
a refresh token.
(C) The client makes a protected resource requests to the resource
server by presenting the access token.

(D) The resource server validates the access token, and if valid,
serves the request.
(E) Steps (C) and (D) repeat until the access token expires. If the
client does not know knows the access token expired, it skips to step (G),
otherwise it makes another protected resource request. Otherwise, it skips to step (G).
(F) Since the access token is invalid (expired), the resource server
returns an invalid token error.
(G) The client requests a new access token by authenticating with
the authorization server using its client credentials, and
presenting the refresh token (as the access grant). token.
(H) The authorization server validates the client credentials and
the refresh token, and if valid issues a new access token (and
optionally, a new refresh token).

1.4.5. Assertion

Assertions provide a bridge between OAuth

1.5. Notational Conventions

The key words 'MUST', 'MUST NOT', 'REQUIRED', 'SHALL', 'SHALL NOT',
'SHOULD', 'SHOULD NOT', 'RECOMMENDED', 'MAY', and other 'OPTIONAL' in this
specification are to be interpreted as described in [RFC2119].

This specification uses the Augmented Backus-Naur Form (ABNF)
notation of [I-D.ietf-httpbis-p1-messaging]. Additionally, the
following rules are included from [RFC3986]: URI-reference; and from
[I-D.ietf-httpbis-p1-messaging]: OWS, RWS, and quoted-string.

Unless otherwise noted, all the protocol parameter names and values
are case sensitive.

2. Client Authentication

Client credentials are used to identify and authenticate the client.
The client credentials include a client identified - a unique string
issued to the client to identify itself to the authorization server.
The methods through which the client obtains its client credentials
are beyond the scope of this specification.

Due to the nature of some clients, the authorization server SHOULD
NOT make assumptions about the confidentiality of client credentials
without establishing trust frameworks.
They enable with the client. The authorization server
SHOULD NOT issue client credentials to utilize clients incapable of keeping
their secrets confidential.

2.1. Client Password Authentication

The client password authentication uses a shared symmetric secret to
authenticate the client. The client identifier and password are
included in the request using the following parameters:

client_id
REQUIRED. The client identifier.
client_secret
REQUIRED. The client password.

For example (line breaks are for display purposes only):

POST /token HTTP/1.1
Host: server.example.com
Content-Type: application/x-www-form-urlencoded

grant_type=authorization_code&client_id=s6BhdRkqt3&
client_secret=gX1fBat3bV&code=i1WsRn1uB1&
redirect_uri=https%3A%2F%2Fclient%2Eexample%2Ecom%2Fcb

2.2. Other Client Authentication Methods

In cases where client password authentication is not suitable or
sufficient, the authorization server MAY support other existing trust relationships HTTP
authentication schemes or define new methods. In addition, the
authorization server MAY allow unauthenticated access token requests
when the client identity does not matter (e.g. anonymous client) or
when the client identity is established via other means.

For example, the authorization server MAY support using the HTTP
Basic authentication scheme as defined in
order [RFC2617] to include the
client identifier as the username and client password as the password
(line breaks are for display purposes only):

POST /token HTTP/1.1
Host: server.example.com
Authorization: Basic czZCaGRSa3F0MzpnWDFmQmF0M2JW
Content-Type: application/x-www-form-urlencoded

grant_type=authorization_code&code=i1WsRn1uB1&
redirect_uri=https%3A%2F%2Fclient%2Eexample%2Ecom%2Fcb

When using a method other than client password authentication to
exchange an authorization code grant type, the authorization server
MUST define a method for mapping the client credentials to the client
identifier used to obtain the authorization code.

3. Protocol Endpoints

The authorization process utilizes two endpoints:

o Authorization endpoint - used to obtain authorization from the
resource owner via user-agent redirection.
o Token endpoint - used to exchange an authorization grant for an
access token. token, typically with client authentication.

Not every authorization grant flow utilizes both endpoints.
Extension grant types MAY define additional endpoints as needed.

3.1. Authorization Endpoint

The authorization endpoint is used to interact with the resource
owner and obtain authorization which is expressed explicitly as an
authorization code (exchanged for an access grant represented token), or implicitly by
direct issuance of an
assertion depends on access token.

The authorization server MUST first verify the assertion type, its content, and how it was
issued, identity of the
resource owner. The way in which are the authorization server
authenticates the resource owner (e.g. username and password login,
session cookies) is beyond the scope of this specification.

Assertions are used as part

The location of the protocol extensibility model,
providing a way for authorization servers endpoint can be found in the
service documentation. The endpoint URI MAY include a query
component as defined by [RFC3986] section 3, which MUST be retained
when adding additional query parameters.

Requests to the authorization endpoint result in user authentication
and the transmission of sensitive information. If the response
includes an access token, the authorization server MUST require TLS
1.2 as defined in [RFC5246] and MAY support additional transport-
layer mechanisms meeting its security requirements. If the response
does not include an access grant types.

2. Client Profiles

[[ add intro token, the authorization server SHOULD
require TLS 1.2 and find new names any additional transport-layer mechanism meeting
its security requirements.

The authorization server MUST support the use of the HTTP "GET"
method for the profiles. this section authorization endpoint, and MAY support the use of the
"POST" method as well.

Parameters sent without a value MUST be treated as if they were
omitted from the request. The authorization server SHOULD ignore
unrecognized request parameters.

3.1.1. Redirection URI

The client directs the resource owner's user-agent to the
authorization endpoint and includes a redirection URI to which the
authorization server will
have normative language redirect the user-agent back once
authorization has been obtained (or denied). The client MAY omit the
redirection URI if one has been established between the client and
authorization server via other means, such as during the client
registration process.

The redirection URI MUST be an absolute URI and MAY include a query
component, which MUST be retained by the authorization server when
adding additional query parameters.

The authorization server SHOULD require the client to pre-register
their redirection URI or at least certain components such as the
scheme, host, port and path. If a redirection URI was registered,
the authorization server MUST compare any redirection URI received at
the authorization endpoint with the registered URI.

The authorization server SHOULD NOT redirect the user-agent to
unregistered or untrusted URIs to prevent the endpoint from being
used as an open redirector. If no valid redirection URI is
available, the authorization server SHOULD inform the resource owner
directly of the error.

3.2. Token Endpoint

The token endpoint is used by the client to obtain an access token by
authenticating with the authorization server and presenting its
authorization grant. The token endpoint is used with every
authorization grant except for the implicit grant type (since an
access token is issued directly).

The location of the token endpoint can be found in future drafts, similar the service
documentation. The endpoint URI MAY include a query component, which
MUST be retained when adding additional query parameters.

Since requests to -05 the token endpoint result in the transmission of
clear-text credentials (in the HTTP request and earlier.
]]

2.1. Web Server response), the
authorization server MUST require the use of a transport-layer
security mechanism when sending requests to the token endpoints. The web
authorization server MUST support TLS 1.2 as defined in [RFC5246],
and MAY support additional transport-layer mechanisms meeting its
security requirements.

The token endpoint requires client authentication as described in
Section 2 . The authorization server MAY accept any form of client
authentication meeting its security requirements. The client MUST
NOT use more than one authentication method in each request.

The client MUST use the HTTP "POST" method when making access token
requests.

Parameters sent without a value MUST be treated as if they were
omitted from the request. The authorization server profile SHOULD ignore
unrecognized request parameters.

4. Requesting an Access Token

The client obtains an access token by requesting authorization from
the resource owner. The authorization is expressed in the form of an
authorization grant which the client exchanges for an access token.
OAuth defines four grant types: authorization code, implicit,
resource owner password credentials, and client credentials, as well
as an extension mechanism for defining additional grant types.

4.1. Authorization Code

The authorization code flow is suitable for clients capable of
maintaining their client credentials confidential (for authenticating
with the authorization server) such as a client implemented on a
secure server. As a redirection-based profile, the client must be
capable of interacting with the end-user's resource owner's user-agent
(typically a web browser) and capable of receiving incoming requests
(via redirection) from the authorization server (capable of acting as an HTTP server). server.

+----------+
| resource |
| owner |
| |
+----------+
^
|
(B)
+----|-----+ Client Identifier +---------------+
| -+----(A)--- & Redirect URI ------>| |
| End-user User- | | Authorization |
| at |<---(B)-- Agent -+----(B)-- User authenticates --->| Server |
| Browser | | |
| -+----(C)-- Authorization Code ---<| |
+-|----|---+ +---------------+
| | ^ v
(A) (C) | |
| | | |
^ v | |
+---------+ | |
| |>---(D)-- Client Credentials, --------' |
| Server | Authorization Code, |
| -Based Client | & Redirect URI |
| Client | |
| |<---(E)----- Access Token -------------------'
+---------+ (w/ Optional Refresh Token)

Figure 5: Web Server 3: Authorization Code Flow

The web server flow illustrated in Figure 5 3 includes the following steps:

(A) The web client initiates the flow by redirecting directing the end-user's resource owner's
user-agent to the end-user authorization endpoint as described
in Section 4. endpoint. The client includes
its client identifier, requested scope, local state, and a redirect
redirection URI to which the authorization server will send the end-user
user-agent back once access is granted (or denied).
(B) The authorization server authenticates the end-user resource owner (via
the user-agent) and establishes whether the end-user resource owner
grants or denies the client's access request.
(C) Assuming the end-user granted resource owner grants access, the authorization
server redirects the user-agent back to the client to using the
redirection URI provided earlier. The authorization redirection URI includes
an authorization code.

(D) The client requests an access token from the authorization
server's token endpoint by authenticating using its client
credentials, and includes the authorization code for received in the
previous step.
(E) The authorization server validates the client credentials and
the authorization code and if valid, responds back with an
access token.

4.1.1. Authorization Request

The client constructs the request URI by adding the following
parameters to use the query component of the authorization endpoint URI
using the "application/x-www-form-urlencoded" format as defined by
[W3C.REC-html401-19991224]:

response_type
REQUIRED. Value MUST be set to obtain "code".
client_id
REQUIRED. The client identifier as described in Section 2.
redirect_uri
REQUIRED, unless a redirection URI has been established between
the client and authorization server via other means. Described
in Section 3.1.1.
scope
OPTIONAL. The scope of the access request expressed as a list
of space-delimited strings. The value is 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
token.

(D) range to the requested scope.
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 client requests directs the resource owner to the constructed URI using an
HTTP redirection response, 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 transport-layer security (line breaks are for
display purposes only):

GET /authorize?response_type=code&client_id=s6BhdRkqt3&
redirect_uri=https%3A%2F%2Fclient%2Eexample%2Ecom%2Fcb HTTP/1.1
Host: server.example.com

The authorization server validates the request to ensure all required
parameters are present and valid. 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 redirection URI using an HTTP
redirection response, or by other means available to it via the user-
agent.

4.1.2. Authorization Response

If the resource owner grants the access token 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
redirection URI using the "application/x-www-form-urlencoded" format:

code
REQUIRED. The authorization code generated by the
authorization server. The authorization code SHOULD expire
shortly after it is issued to minimize the risk of leaks. The
client MUST NOT reuse the authorization code. If an
authorization code is used more than once, the authorization
server MAY revoke all tokens previously issued based on that
authorization code. The authorization code is bound to the
client identifier and redirection URI.
state
REQUIRED if the "state" parameter was present in the client
authorization request. Set to the exact value received from
the client.

For example, the authorization server redirects the user-agent by authenticating
sending the following HTTP response:

HTTP/1.1 302 Found
Location: https://client.example.com/cb?code=i1WsRn1uB1

The client SHOULD ignore unrecognized response parameters. The
authorization code string size is left undefined by this
specification. The clients should avoid making assumptions about
code value sizes. The authorization server should document the size
of any value is issues.

4.1.2.1. Error Response

If the request fails due to a missing, invalid, or mismatching
redirection URI, the authorization server SHOULD inform the resource
owner of the error, and including MUST NOT redirect the user-agent to the
invalid redirection URI.

If the resource owner denies the access request or if the request
fails for reasons other than a missing or invalid redirection URI,
the authorization server informs the client by adding the following
parameters to the query component of the redirection URI using the
"application/x-www-form-urlencoded" format:

error
REQUIRED. A single error code from the following:
invalid_request
The request is missing a required parameter, includes an
unsupported parameter or parameter value, or is otherwise
malformed.
invalid_client
The client identifier provided is invalid.
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.
error_description
OPTIONAL. A human-readable text providing additional
information, used to assist in the understanding and resolution
of the error occurred.
error_uri
OPTIONAL. A URI identifying a human-readable web page with
information about the error, used to provide the resource owner
with additional information about the error.
state
REQUIRED if the "state" parameter was present in the client
authorization request. Set to the exact value received from
the client.

For example, the authorization server redirects the user-agent by
sending the following HTTP response:

HTTP/1.1 302 Found
Location: https://client.example.com/cb?error=access_denied

4.1.3. Access Token Request

The client makes a request to the token endpoint by adding the
following parameter using the "application/x-www-form-urlencoded"
format in the HTTP request entity-body:

grant_type
REQUIRED. Value MUST be set to "authorization_code".
code
REQUIRED. The authorization code received from the
authorization server.
redirect_uri
REQUIRED. The redirection URI used in the previous step initial request.

The client includes its authentication credentials as described in
Section 5.

(E) 2

For example, the client makes the following HTTP request by including
its client credentials via the "client_id" and "client_secret"
parameters, and using transport-layer security (line breaks are for
display purposes only):

POST /token HTTP/1.1
Host: server.example.com
Content-Type: application/x-www-form-urlencoded

grant_type=authorization_code&client_id=s6BhdRkqt3&
client_secret=gX1fBat3bV&code=i1WsRn1uB1&
redirect_uri=https%3A%2F%2Fclient%2Eexample%2Ecom%2Fcb

The authorization server validates MUST:

o Validate the client credentials and ensure they match the
authorization code.
o Verify that the authorization code and responds back with redirection URI are valid
and match its stored association.

If the request is valid and authorized, the authorization server
issues an access token.

2.2. User-Agent token and optional refresh token, and responds as
described in Section 5.

4.2. Implicit Grant

The user-agent profile implicit grant flow is suitable for clients incapable of
maintaining their client credentials confidential (for authenticating
with the authorization server) such as client applications residing
in a user-agent, typically implemented in a browser using a scripting
language such as JavaScript. JavaScript, or native applications. These clients
cannot keep client secrets confidential and the authentication of the
client is based on the user-agent's same-origin policy.

As a redirection-based profile, the client must be capable of
interacting with the resource owner's user-agent (typically a web
browser) and capable of receiving incoming requests (via redirection)
from the authorization server.

Unlike other profiles the authorization code flow in which the client makes separate
requests for
end-user authorization and access token, the client receives the
access token as a the result of the end-user authorization request in the
form of an HTTP redirection. request.

The client requests the authorization
server to redirect the user-agent to another web server or local
resource accessible to the user-agent which is capable of extracting
the access token from the response and passing it to the client.

This user-agent profile implicit grant flow does not utilize the client secret credentials since
the client executables reside is unable to maintain their confidentiality (the client
resides on the end-user's resource owner's computer or device which makes the
client secret credentials accessible and exploitable. exploitable). Because the access
token is encoded into the redirection URI, it may be exposed to the end-user
resource owner and other applications residing on the its computer or
device.

+----------+
| Resource |
| Owner |
| |
+----------+
^
|
(B)
+----|-----+ Client Identifier +----------------+ +---------------+
| |>---(A)-- -+----(A)--- & Redirection Redirect URI --->| ----->| |
| User- | | Authorization |
End <--+ - - - +----(B)--
| Agent -|----(B)-- User authenticates -->| Authorization Server |
User
| | | Server |
| |<---(C)--- |<---(C)---- Redirect URI -------<| ------<| |
| Client | with Access Token +---------------+
| |
| in | in Fragment +----------------+
| Browser | +---------------+
| | +----------------+
| |>---(D)--- |----(D)---- Redirect URI ------->| ------>| Web Server |
| | without Fragment | Web Server with Client |
| | | with Client Resource |
| (F) |<---(E)--- Web Page with ------<| Resource |<---(E)------- Script ---------<| |
| | +---------------+
+-|--------+
| |
(A) (G) Access Token
| Script |
^ v
+---------+
| | Token
| +----------------+
+----------+ Client |
| |
+---------+

Figure 6: User-Agent 4: Implicit Grant Flow

The user-agent flow illustrated in Figure 6 4 includes the following steps:

(A) The client sends initiates the flow by directing the resource owner's
user-agent to the end-user authorization
endpoint as described in Section 4. endpoint. The client includes
its client identifier, requested scope, local state, and a redirect
redirection URI to which the authorization server will send the end-user
user-agent back once authorization access is granted (or denied).
(B) The authorization server authenticates the end-user resource owner (via
the user-agent) and establishes whether the end-user resource owner
grants or denies the client's access request.

(C) If Assuming the end-user granted resource owner grants access, the authorization
server redirects the user-agent back to the client using the
redirection URI provided earlier. The redirection URI includes
the access token in the URI fragment.
(D) The user-agent follows the redirection instructions by making a
request to the web server which does (does not include the fragment. fragment). The
user-agent retains the fragment information locally.
(E) The web server returns a web page (typically an HTML page document
with an embedded script) capable of accessing the full
redirection URI including the fragment retained by the user-agent, user-
agent, and extracting the access token (and other parameters)
contained in the fragment.
(F) The user-agent executes the script provided by the web server
locally, which extracts the access token and passes it to the
client.

2.3. Native Application

Native applications are clients running as native code on the end-
user's computer or device (i.e. executing outside a user-agent or as
a desktop program). These clients are often capable of interacting
with (or embedding) the end-user's user-agent but are limited in how
such interaction affects their end-user experience. In many cases,
native applications are incapable of receiving direct callback
requests from the server (e.g. firewall, operating system
restrictions).

Native application clients can be implemented in different ways based
on their requirements and desired end-user experience. Native
application clients can:

o Utilize the end-user authorization endpoint as described in
Section 4 by launching an external user-agent. The client can
capture the response by providing a redirection URI with a custom
URI scheme (registered with the operating system to invoke the
client application), or by providing a redirection URI pointing to
a server-hosted resource under the client's control which makes
the response available to the client (e.g. using the window title
or other locations accessible from outside the user-agent).

o Utilize the end-user authorization endpoint as described in
Section 4 by using an embedded user-agent. The client obtains the
response by directly communicating with the embedded user-agent.

o Prompt end-users for their password and use them directly to
obtain an access token. This is generally discouraged, as it
hands the end-user's password directly to the third-party client
which in turn has to store it in clear-text. It also requires the
server to support password-based authentication.

When choosing between launching an external browser and an embedded
user-agent, developers should consider the following:

o External user-agents may improve completion rate as the end-user
may already be logged-in and not have to re-authenticate.

o Embedded user-agents often offer a better end-user flow, as they
remove the need to switch context and open new windows.

o Embedded user-agents pose a security challenge because users are
authenticating in an unidentified window without access to the
visual protections offered by many user-agents.

2.4. Autonomous

Autonomous clients utilize an existing trust relationship or
framework to establish authorization. Autonomous clients can be
implemented in different ways based on their requirements and the
existing trust framework they rely upon. Autonomous clients can:

o Obtain an access token by authenticating with the authorization
server using their client credentials. The scope of the access
token is limited to the protected resources under the control of
the client, or that of another resource owner previously arranged
with the authorization server.

o Use an existing access grant expressed as an assertion using an
assertion format supported by the authorization server. Using
assertions requires the client to obtain an assertion (such as a
SAML [OASIS.saml-core-2.0-os] assertion) from an assertion issuer
or to self-issue an assertion. The assertion format, the process
by which the assertion is obtained, and the method of validating
the assertion are defined by the assertion issuer and the
authorization server, and are beyond the scope of this
specification.

3. Client Credentials

When interacting with the authorization server, the client identifies
itself using a set of client credentials which include a client
identifier and other properties for client authentication. The means
through which the client obtains its credentials are beyond the scope
of this specification, but typically involve registration with the
authorization server.

Due to the nature of some clients, authorization servers SHOULD NOT
make assumptions about the confidentiality of client secrets without
establishing trust with the client. Authorization servers SHOULD NOT
issue client secrets to clients incapable of keeping their secrets
confidential.

The authorization server MAY authenticate the client using any
appropriate set of credentials and authentication schemes. The
client MUST NOT include more than one set of credentials or
authentication mechanism with each request.

3.1. Client Password Credentials

The client password credentials use a shared symmetric secret to
authenticate the client. The client identifier and password are
included in the request using the HTTP Basic authentication scheme as
defined in [RFC2617] by including the client identifier as the
username and client password as the password.

For example (line breaks are for display purposes only):

POST /token HTTP/1.1
Host: server.example.com
Authorization: Basic czZCaGRSa3F0MzpnWDFmQmF0M2JW
Content-Type: application/x-www-form-urlencoded

grant_type=authorization_code&code=i1WsRn1uB1&
redirect_uri=https%3A%2F%2Fclient%2Eexample%2Ecom%2Fcb

Alternatively, the client MAY include the password in the request
body using the following parameters:

client_id
REQUIRED. The client identifier.

client_secret REQUIRED. The client password.

For example (line breaks are for display purposes only):

POST /token HTTP/1.1
Host: server.example.com
Content-Type: application/x-www-form-urlencoded

grant_type=authorization_code&client_id=s6BhdRkqt3&
client_secret=gX1fBat3bV&code=i1WsRn1uB1&
redirect_uri=https%3A%2F%2Fclient%2Eexample%2Ecom%2Fcb

The authorization server MUST accept the client credentials using
both the request parameter, and the HTTP Basic authentication scheme.
The authorization server MAY support additional authentication
schemes suitable for the transmission of password credentials.

3.2. Client Assertion Credentials

The client assertion credentials are used in cases where a password
(clear-text shared symmetric secret) is unsuitable or does not
provide sufficient security for client authentication. In such cases
it is common to use other mechanisms such as HMAC or digital
signatures that do not require sending clear-text secrets. The
client assertion credentials provide an extensible mechanism to use
an assertion format supported by the authorization server for
authentication the client.

Using assertions requires the client to obtain an assertion (such as
a SAML [OASIS.saml-core-2.0-os] assertion) from an assertion issuer
or to self-issue an assertion. The assertion format, the process by
which the assertion is obtained, and the method of validating the
assertion are defined by the assertion issuer and the authorization
server, and are beyond the scope of this specification.

When using a client assertion, the client includes the following
parameters:

client_assertion_type REQUIRED. The format of the assertion as
defined by the authorization server. The value MUST be an
absolute URI.

client_assertion REQUIRED. The client assertion.

For example, the client sends the following access token request
using a SAML 2.0 assertion to authenticate itself (line breaks are
for display purposes only):

POST /token HTTP/1.1
Host: server.example.com
Content-Type: application/x-www-form-urlencoded

grant_type=authorization_code&code=i1WsRn1uB1&
client_assertion=PHNhbWxwOl[...omitted for brevity...]ZT4%3D&
client_assertion_type=
urn%3Aoasis%3Anames%sAtc%3ASAML%3A2.0%3Aassertion&
redirect_uri=https%3A%2F%2Fclient%2Eexample%2Ecom%2Fcb

When obtaining an access token using a client assertion together with
an authorization code (as described in Section 5.1.1), a mechanism is
needed to map between the value of "client_id" parameter used to
obtain the authorization code, and the client assertion. Such
mechanism is beyond the out of scope for this specification, but MUST
be specified for any client assertion type used in combination with
an authorization code.

The authorization server MUST reject access token requests using
client assertion credentials that do not contain HMAC or signed
values that:

o State the assertion was specifically issued to be consumed by the
receiving endpoint (typically via an audience or recipient value
containing the receiving endpoint's identifier).

o Identify the entity that issued the assertion (typically via an
issuer value).

o Identify when the assertion expires as an absolute time (typically
via an expiration value containing a UTC date/time value). The
authorization server MUST reject expired assertions.

4. Obtaining End-User Authorization

Before the client can access a protect resource, it MUST first obtain
authorization from the end-user. To obtain an end-user
authorization, the client sends the end-user to the end-user
authorization endpoint. Once obtained, the end-user access grant is
expressed as an authorization code which the client uses to obtain an
access token.

At the end-user authorization endpoint, the end-user first
authenticates with the authorization server, and then grants or
denies the access request. The way in which the authorization server
authenticates the end-user (e.g. username and password login, OpenID,
session cookies) and in which the authorization server obtains the
end-user's authorization, including whether it uses a secure channel
such as TLS, is beyond the scope of this specification. However, the
authorization server MUST first verify the identity of the end-user.

The location of the end-user authorization endpoint can be found in
the service documentation. The end-user authorization endpoint URI
MAY include a query component as defined by [RFC3986] section 3,
which must be retained when adding additional query parameters.

Since requests to the end-user authorization endpoint result in user
authentication and the transmission of sensitive information, the
authorization server SHOULD require the use of a transport-layer
security mechanism such as TLS when sending requests to the end-user
authorization endpoint.

4.1.

4.2.1. Authorization Request

In order to direct the end-user's user-agent to the authorization
server, the

The client constructs the request URI by adding the following
parameters to the end-user query component of the authorization endpoint URI query component
using the "application/x-www-form-urlencoded" format as defined by
[W3C.REC-html401-19991224]: format:

response_type
REQUIRED. The requested response: an access token, an
authorization code, or both. The parameter value Value MUST be set to "token" for requesting an access token, "code" for
requesting an authorization code, or "code_and_token" to
request both. The authorization server MAY decline to provide
one or more of these response types. "token".
client_id
REQUIRED. The client identifier as described in Section 3. 2.
Due to lack of client authentication, the client identifier
alone MUST NOT be relied upon for client identification.
redirect_uri
REQUIRED, unless a redirection URI has been established between
the client and authorization server via other means. An
absolute URI to which the authorization server will redirect
the user-agent to when the end-user authorization step is
completed. The authorization server SHOULD require the client
to pre-register their redirection URI. Described
in Section 3.1.1.
scope
OPTIONAL. The scope of the access request expressed as a list
of space-delimited strings. The value of the "scope" parameter is defined by the
authorization server. If the value contains multiple space-delimited space-
delimited strings, their order does not matter, and each string
adds an additional access range to the requested scope.
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 client directs the end-user to the constructed URI using an HTTP
redirection response, or by other means available to it via the end-
user's user-agent. The authorization server MUST support the use of
the HTTP "GET" method for the end-user authorization endpoint, and
MAY support the use of the "POST" method as well.

For example, the client directs the end-user's user-agent to make the
following HTTP request using transport-layer security (line breaks
are for display purposes only):

GET /authorize?response_type=code&client_id=s6BhdRkqt3&
redirect_uri=https%3A%2F%2Fclient%2Eexample%2Ecom%2Fcb HTTP/1.1
Host: server.example.com

If the client has previously registered a redirection URI with the
authorization server, the authorization server MUST verify that the
redirection URI received matches the registered URI associated with
the client identifier. The authorization server SHOULD NOT redirect
the user-agent to unregistered or untrusted URIs resource owner to prevent the
endpoint from being used as constructed URI using an open redirector. If no valid
HTTP redirection URI is available, response, or by other means available to it via the authorization server SHOULD inform
user-agent.

For example, the end-user of client directs the error occured. [[ provide guidance on how user-agent to
perform matching ]]

Parameters sent without a value MUST be treated as if they were
omitted from make the request. The authorization server SHOULD ignore
unrecognized following
HTTP request parameters. using transport-layer security (line breaks are for
display purposes only):

GET /authorize?response_type=token&client_id=s6BhdRkqt3&
redirect_uri=https%3A%2F%2Fclient%2Eexample%2Ecom%2Fcb HTTP/1.1
Host: server.example.com

The authorization server validates the request to ensure all required
parameters are present and valid. If the request is invalid, the
authorization server redirects the user-agent back to the client
using the redirection URI provided with valid, the appropriate error code as
described in Section 4.3.

The
authorization server authenticates the end-user resource owner and obtains an
authorization decision (by asking the end-user resource owner or by
establishing approval via other means).

When a decision has been is established, the authorization server directs the end-user's
user-agent to the provided client redirection URI using an HTTP
redirection response, or by other means available to it via the end-user's user-agent.

4.2. Authorization user-
agent.

4.2.2. Access Token Response

If the end-user resource owner grants the access request, the authorization
server issues an access token, an authorization code, or both, token and delivers
them it to the client by adding
the following parameters to the
redirection URI (as described below):

code
REQUIRED if the response type is "code" or "code_and_token",
otherwise MUST NOT be included. The authorization code
generated by the authorization server. The authorization code
SHOULD expire shortly after it is issued to minimize the risk fragment component of leaks. The client MUST NOT reuse the authorization code.
If an authorization code is used more than once, the
authorization server MAY revoke all tokens previously issued
based on that authorization code. The authorization code is
bound to the client identifier and redirection URI.

access_token
REQUIRED if
URI using the response type is "token" or "code_and_token",
otherwise MUST NOT be included. "application/x-www-form-urlencoded" format:

access_token
REQUIRED. The access token issued by the authorization server.
token_type
REQUIRED if the response includes an access token.
REQUIRED. The type of the token issued. The token type informs the client how the
access token is to be used when accessing a protected resource issued as described in
Section 6.1. 7.1. Value is case insensitive.
expires_in
OPTIONAL. The duration in seconds of the access token lifetime
if an access token is included.
lifetime. For example, the value "3600" denotes that the
access token will expire in one hour from the time the response
was generated by the authorization server. generated.
scope
OPTIONAL. The scope of the access token request expressed as a list
of space-
delimited strings if an access token is included. space-delimited strings. The value of
the "scope" parameter is defined by the
authorization server. If the value contains multiple space-delimited space-
delimited strings, their order does not matter, and each string
adds an additional access range to the requested scope. The
authorization server SHOULD include the parameter if the
requested scope is different from the one requested by the
client.

state
REQUIRED if the "state" parameter was present in the client
authorization request. Set to the exact value received from
the client.

The method in which the authorization server adds the parameter to
the redirection URI is determined by the response type requested by
the client in the authorization request using the "response_type"
parameter.

If the response type is "code", the authorization server adds the
parameters to the redirection URI query component using the
"application/x-www-form-urlencoded" format as defined by
[W3C.REC-html401-19991224].

For example, the authorization server redirects the end-user's user-
agent by sending the following HTTP response:

HTTP/1.1 302 Found
Location: https://client.example.com/cb?code=i1WsRn1uB1

If the response type is "token" or "code_and_token", the
authorization server adds the parameters to the redirection URI
fragment component using the "application/x-www-form-urlencoded"
format as defined by [W3C.REC-html401-19991224].

For example, the authorization server redirects the end-user's user-
agent user-agent by
sending the following HTTP response (URI line breaks are for display
purposes only):

HTTP/1.1 302 Found
Location: http://example.com/rd#access_token=FJQbwq9&
token_type=example&expires_in=3600

Clients

The client SHOULD ignore unrecognized response parameters. The sizes of
tokens and other values received from the authorization server, are
access token string size is left undefined by this specification. Clients
The client should avoid making assumptions about value sizes. Servers The
authorization server should document the expected size of any value they issue.

4.3. it issues.

4.2.2.1. Error Response

If the end-user request fails due to a missing, invalid, or mismatching
redirection URI, the authorization server SHOULD inform the resource
owner of the error, and MUST NOT redirect the user-agent to the
invalid redirection URI.

If the resource owner denies the access request or if the request
fails for reasons other than a missing or invalid redirection URI,
the authorization server informs the client by adding the following
parameters to the fragment component of the redirection URI query component using the
"application/x-www-form-urlencoded" format as defined by
[W3C.REC-html401-19991224]: format:

error
REQUIRED. A single error code as described in Section 4.3.1. from the following:
invalid_request
The request is missing a required parameter, includes an
unsupported parameter or parameter value, or is otherwise
malformed.
invalid_client
The client identifier provided is invalid.
unauthorized_client
The client is not authorized to request an access token
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
access token using this method.
invalid_scope
The requested scope is invalid, unknown, or malformed.
error_description
OPTIONAL. A human-readable text providing additional
information, used to assist in the understanding and resolution
of the error occurred.
error_uri
OPTIONAL. A URI identifying a human-readable web page with
information about the error, used to provide the end-user resource owner
with additional information about the error.
state
REQUIRED if the "state" parameter was present in the client
authorization request. Set to the exact value received from
the client.

For example, the authorization server redirects the end-user's user-
agent user-agent by
sending the following HTTP response:

HTTP/1.1 302 Found
Location: https://client.example.com/cb?error=access_denied

If the request fails due to a missing or invalid redirection URI, the
authorization server SHOULD inform the end-user of the error, and
MUST NOT redirect the end-user's user-agent to the invalid
redirection URI.

4.3.1. Error Codes https://client.example.com/cb#error=access_denied

4.3. Resource Owner Password Credentials

The authorization server includes one of resource owner password credentials flow is suitable in cases
where the following error codes resource owner has a trust relationship with the error response:

invalid_request
The request is missing a required parameter, includes an
unsupported parameter or parameter value, client,
such as its computer operating system or is otherwise
malformed.

invalid_client
The client identifier provided is invalid.

unauthorized_client
The client is not authorized to use the requested response
type.

redirect_uri_mismatch
The redirection URI provided does not match a pre-registered
value.

access_denied highly privileged
application. The end-user or authorization server denied should take special care when
enabling the request.

unsupported_response_type
The requested response type is flow, and only when other flows are not supported by the
authorization server.

invalid_scope viable.

The requested scope flow is invalid, unknown, or malformed.

[[ Add mechanism suitable for extending error codes ]]

5. Obtaining an Access Token

The client obtains an access token by authenticating with the
authorization server and presenting its access grant (in the form clients capable of
an authorization code, obtaining the resource
owner credentials, credentials (username and password, typically using an assertion,
interactive form). It is also used to migrate existing clients using
direct authentication schemes such as HTTP Basic or a
refresh token).

Since requests Digest
authentication to OAuth by converting the token endpoint result in the transmission of
clear-text stored credentials in with an
access token.

The method through which the HTTP request and response, client obtains the
authorization server MUST require resource owner
credentials is beyond the use scope of a transport-layer
security mechanism when sending requests to the token endpoints.
Servers MUST support TLS 1.2 as defined in [RFC5246], and MAY support
additional transport-layer security mechanisms. this specification. The client requests
MUST discard the credentials once an access token by making an HTTP "POST" request
to the token endpoint. has been obtained.

Figure 5: Resource Owner Password Credentials Flow

The location of the token endpoint can be
found flow illustrated in Figure 5 includes the service documentation. The token endpoint URI MAY
include a query component. following steps:

(A) The resource owner provides the client authenticates with its username and
password.
(B) The client requests an access token from the authorization server
server's token endpoint by adding authenticating using its client
credentials, and includes the credentials to received from the request as described in Section 3.
resource owner.
(C) The authorization server MAY allow unauthenticated access token requests
when validates the client identity does not matter (e.g. anonymous client) or
when resource owner
credentials and the client identity is established via other means (e.g. using credentials and issues an assertion access grant).
token.

4.3.1. Access Token Request

The client constructs the makes a request to the token endpoint by including adding the
following
parameters parameter using the "application/x-www-form-urlencoded"
format in the HTTP request entity-body:

grant_type
REQUIRED. The access grant type included in the request. Value MUST be one of "authorization_code", "password",
"refresh_token", "client_credentials", or an absolute URI
identifying an assertion format supported by the authorization
server. set to "password".
username
REQUIRED. The resource owner username.

password
REQUIRED. The resource owner password.
scope
OPTIONAL. The scope of the access request expressed as a list
of space-delimited strings. The value of the "scope" parameter is defined by the
authorization server. If the value contains multiple space-delimited space-
delimited strings, their order does not matter, and each string
adds an additional access range to the requested scope. If the access grant being used already
represents an approved scope (e.g. authorization code,
assertion), the requested scope MUST be equal or lesser than
the scope previously granted, and if omitted is treated as
equal to the previously approved scope.

In addition, the client MUST include the appropriate parameters
listed for the selected access grant type as described in
Section 5.1.

Parameters sent without a value MUST be treated as if they were
omitted from the request. The authorization server SHOULD ignore
unrecognized request parameters.

5.1. Access Grant Types

The client requests an access token using an authorization code,
resource owner password credentials, client credentials, refresh
token, or assertion.

5.1.1. Authorization Code

The client includes the authorization code using the
"authorization_code" access grant type and the following parameters:

code
REQUIRED. The authorization code received from the
authorization server.

redirect_uri
REQUIRED. The redirection URI used in the initial request.

For example, the client makes the following HTTP request by including its client credentials via the "client_secret" parameter described in
Section 3 and using transport-layer security (line breaks are for
display purposes only):

POST /token HTTP/1.1
Host: server.example.com
Content-Type: application/x-www-form-urlencoded

grant_type=authorization_code&client_id=s6BhdRkqt3&
client_secret=gX1fBat3bV&code=i1WsRn1uB1&
redirect_uri=https%3A%2F%2Fclient%2Eexample%2Ecom%2Fcb

The authorization server MUST:

o Validate the client authentication credentials (if present) and ensure they match
the authorization code.

o Verify that the authorization code and redirection URI are all
valid and match its stored association.

If the request is valid, the authorization server issues a successful
response as described in
Section 5.2.

5.1.2. Resource Owner Password Credentials

The client includes the resource owner credentials using the
"password" access grant type and the following parameters: 2

[[ add internationalization consideration for username and password
]]

username
REQUIRED. The resource owner's username.

password
REQUIRED. The resource owner's password.

For example, the client makes the following HTTP request by including
its client credentials via the "client_id" and "client_secret" parameter described in
Section 3
parameters, and using transport-layer security (line breaks are for
display purposes only):

POST /token HTTP/1.1
Host: server.example.com
Content-Type: application/x-www-form-urlencoded

grant_type=password&client_id=s6BhdRkqt3&
client_secret=47HDu8s&username=johndoe&password=A3ddj3w

The authorization server MUST validate MUST:

o Validate the client credentials (if
present) and end-user credentials and if credentials.
o Validate the resource owner password credentials.

If the request is valid issue and authorized, the authorization server
issues an access token
response and optional refresh token, and responds as
described in Section 5.2.

5.1.3. 5.

4.4. Client Credentials

The client can request an access token using only its client
credentials using the "client_credentials" access grant type. When
omitting an explicit access grant, when the client is requesting access to the protected
resources under its control, or those of another resource owner which
has been previously arranged with the authorization server (the
method of which is beyond the scope of this specification).

5.1.4. Refresh

Figure 6: Client Credentials Flow

The client flow illustrated in Figure 6 includes the refresh following steps:

(A) The client requests an access token from the token endpoint by
authenticating using its client credentials.
(B) The authorization server validates the "refresh_token"
access grant type client credentials and
issues an access token.

4.4.1. Access Token Request

The client makes a request to the token endpoint by adding the
following parameter:

refresh_token parameter using the "application/x-www-form-urlencoded"
format in the HTTP request entity-body:

grant_type
REQUIRED. Value MUST be set to "client_credentials".
scope
OPTIONAL. The refresh token associated with scope of the access token request expressed as a list
of space-delimited strings. The value is 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 be refreshed. the requested scope.

The client includes its authentication credentials as described in
Section 2

POST /token HTTP/1.1
Host: server.example.com
Content-Type: application/x-www-form-urlencoded

grant_type=refresh_token&client_id=s6BhdRkqt3&
client_secret=8eSEIpnqmM&refresh_token=n4E9O119d

grant_type=client_credentials&client_id=s6BhdRkqt3&
client_secret=47HDu8s

The authorization server MUST verify validate the client credentials (if
present), the validity of the refresh token, and that the resource
owner's authorization is still valid. credentials.

If the request is valid, valid and authorized, the authorization server
issues an access token response and optional refresh token, and responds as
described in Section 5.2. 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.

5.1.5. Assertion 5.

4.5. Extensions

The client includes uses an assertion extension grant type by specifying the assertion format grant type
using an absolute URI (as defined (defined by the authorization server) as the
value of the "grant_type" parameter of the token endpoint, and by
adding the following
parameter:

assertion
REQUIRED. The assertion. any additional parameters necessary.

For example, to request an access token using a SAML 2.0 assertion
grant type, the client makes the following HTTP request using
transport-layer security, and client authentication is achieved via
the assertion security (line breaks are for display purposes only):

POST /token HTTP/1.1
Host: server.example.com
Content-Type: application/x-www-form-urlencoded

grant_type=urn%3Aoasis%3Anames%3Atc%3ASAML%3A2.0%3Aassertion&
assertion=PHNhbWxwOl[...omitted

grant_type=http%3A%2F%2Foauth.net%2Fgrant_type%2Fassertion%2F
saml%2F2.0%2Fbearer&assertion=PEFzc2VydGlvbiBJc3N1ZUluc3RhbnQ
[...omitted for brevity...]ZT4%3D

The authorization server MUST validate the client credentials (if
present) brevity...]V0aG5TdGF0ZW1lbnQ-PC9Bc3NlcnRpb24-

Client authentication and the scope of the grant are obtained via the
assertion and if as defined by [I-D.ietf-oauth-saml2-bearer].

5. Issuing an Access Token

If the access token request is valid and authorized, the
authorization server issues an access token
response and optional refresh
token as described in Section 5.2. The authorization server
SHOULD NOT issue a refresh token (instead, it should require 5.1. If the request failed client to use the same
authentication or new assertion).

Authorization servers SHOULD issue access tokens with a limited
lifetime and require clients to refresh them by requesting a new
access token using the same assertion if it is still valid.
Otherwise invalid, the client MUST obtain a new valid assertion. authorization server return an
error response as described in Section 5.2. Access Token

5.1. Successful Response

After receiving and verifying a valid and authorized access token
request from the client, the

The authorization server issues the an access token and optional refresh
token, and constructs the response by adding the following parameters
to the entity body of the HTTP response with a 200 (OK) status code:

The token response contains the following parameters:

access_token
REQUIRED. The access token issued by the authorization server.
token_type
REQUIRED. The type of the token issued. The token type
informs the client how the access token is to be used when
accessing a protected resource issued as described in
Section 6.1. 7.1. Value is case insensitive.
expires_in
OPTIONAL. The duration in seconds of the access token
lifetime. For example, the value "3600" denotes that the
access token will expire in one hour from the time the response
was generated by the authorization server. generated.
refresh_token
OPTIONAL. The refresh token which can be used to obtain new
access tokens using the same end-user access authorization grant as described
in Section 5.1.4. The authorization server SHOULD NOT issue a
refresh token when the access grant type is an assertion or a
set of client credentials. 6.
scope
OPTIONAL. The scope of the access token request expressed as a list
of space-
delimited space-delimited strings. The value of the "scope" parameter is defined by the
authorization server. If the value contains multiple space-delimited space-
delimited strings, their order does not matter, and each string
adds an additional access range to the requested scope. The
authorization server SHOULD include the parameter if the
requested scope is different from the one requested by the
client.

The parameters are including in the entity body of the HTTP response
using the "application/json" media type as defined by [RFC4627]. 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 authorization server MUST include the HTTP "Cache-Control"
response header field with a value of "no-store" in any response
containing tokens, secrets, or other sensitive information.

For example:

HTTP/1.1 200 OK
Content-Type: application/json
Cache-Control: no-store

{
"access_token":"SlAV32hkKG",
"token_type":"example",
"expires_in":3600,
"refresh_token":"8xLOxBtZp8"
"refresh_token":"8xLOxBtZp8",
"example_parameter":"example-value"

}

Clients

The client SHOULD ignore unrecognized response parameters. The sizes
of tokens and other values received from the authorization server, server are
left undefined by this specification. Clients undefined. The client should avoid making assumptions about
value sizes. Servers The authorization server should document the expected size of
any value they issue.

5.3. it issues.

5.2. Error Response

If the token request is invalid or unauthorized, the authorization
server constructs the response by adding the following parameter to
the entity body of the HTTP response using the "application/json"
media type:

error
REQUIRED. A single error code as described in Section 5.3.1.

error_description OPTIONAL. A human-readable text providing
additional information, used to assist in the understanding and
resolution of the error occurred.

error_uri OPTIONAL. A URI identifying a human-readable web page
with information about the error, used to provide the end-user
with additional information about the error.

For example:

HTTP/1.1 400 Bad Request
Content-Type: application/json
Cache-Control: no-store

{
"error":"invalid_request"
}

If the client provided invalid credentials using an HTTP
authentication scheme via the "Authorization" request header field,
the authorization server MUST respond with the a HTTP 401 (Unauthorized)
status code. code, and include the "WWW-Authenticate" response header field
matching the authentication scheme used by the client. Otherwise,
the authorization server
SHALL MUST respond with the HTTP 400 (Bad Request)
status code.

5.3.1. Error Codes

The authorization server includes one of constructs the response by adding the
following error codes
with parameter to the error response:

error
REQUIRED. A single error code from the following:
invalid_request
The request is missing a required parameter, includes an
unsupported parameter or parameter value, repeats a
parameter, includes multiple credentials, utilizes more
than one mechanism for authenticating the client, or is
otherwise malformed.
invalid_client
The client identifier provided is invalid, the client
Client authentication failed to
authenticate, the (e.g. unknown client, no
client did not include its credentials,
provided credentials included, multiple client credentials, credentials
included, or used unsupported credentials type.

unauthorized_client
The authenticated client is not authorized to use the access
grant type provided. type).
invalid_grant
The provided access authorization grant is invalid, expired,
revoked, or revoked (e.g.
invalid assertion, expired does not match the redirection URI used in
the authorization token, bad end-user
password credentials, or mismatching request.
unauthorized_client
The authenticated client is not authorized to use this
authorization code and
redirection URI). grant type.
unsupported_grant_type
The access authorization grant included - its type or another attribute - is not supported by the
authorization server.

invalid_scope
The requested scope is invalid, unknown, malformed, or
exceeds the previously granted scope.

[[ Add mechanism for extending
error_description
OPTIONAL. A human-readable text providing additional
information, used to assist in the understanding and resolution
of the error codes ]] occurred.
error_uri
OPTIONAL. A URI identifying a human-readable web page with
information about the error, used to provide the resource owner
with additional information about the error.

For example:

HTTP/1.1 400 Bad Request
Content-Type: application/json
Cache-Control: no-store

{
"error":"invalid_request"
}

6. Accessing Refreshing an Access Token

The client makes a Protected Resource

Clients request to the token endpoint by adding the
following parameter using the "application/x-www-form-urlencoded"
format in the HTTP request entity-body:

grant_type
REQUIRED. Value MUST be set to "refresh_token".
refresh_token
REQUIRED. The refresh token issued along the access token
being refreshed.
scope
OPTIONAL. The scope of the access request expressed as a list
of space-delimited strings. The value is 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
requested scope MUST be equal or lesser than the scope
originally granted by the resource owner, and if omitted is
treated as equal to the previously approved scope.

The client includes its authentication credentials as described in
Section 2

POST /token HTTP/1.1
Host: server.example.com
Content-Type: application/x-www-form-urlencoded

grant_type=refresh_token&client_id=s6BhdRkqt3&
client_secret=8eSEIpnqmM&refresh_token=n4E9O119d

The authorization server MUST validate the client credentials, the
refresh token, and verify that the resource owner's authorization is
still valid. If valid, the authorization server issues an access
token response as described in Section 5.

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.

7. Accessing Protected Resources

The client accesses protected resources by presenting an the access
token to the resource server. The resource server MUST validate the
access token and ensure it has not expired and that its scope covers
the requested resource. The methods used by the resource server to
validate the access token are beyond the scope of this specification,
but generally involve an interaction or coordination between the
resource server and the authorization server.

The method in which the client utilized the access token to
authenticate with the resource server depends on the type of access
token issued by the authorization server.

6.1. Access Token Types

[[ add token type explanation, maybe with links to other token specs
]]

6.2. The WWW-Authenticate Response Header Field

If the protected resource request does not include authentication
credentials, contains an invalid access token, or is malformed, the
resource server MUST include Typically, it involves
using the HTTP "WWW-Authenticate" response
header field. The "WWW-Authenticate" "Authorization" request header field uses the framework with an
authentication scheme defined by [RFC2617] as follows:

challenge = "OAuth2" [ RWS 1#param ]

param = scope /
error / error-desc / error-uri /
( token "=" ( token / quoted-string ) )

scope = "scope" "=" <"> scope-v *( SP scope-v ) <">
scope-v = 1*quoted-char

quoted-char = ALPHA / DIGIT /
"!" / "#" / "$" / "%" / "&" / "'" / "(" / ")" /
"*" / "+" / "-" / "." / "/" / ":" / "<" / "=" /
">" / "?" / "@" / "[" / "]" / "^" / "_" / "`" /
"{" / "|" / "}" / "~" / "\" / "," / ";"

error = "error" "=" quoted-string
error-desc = "error_description" "=" quoted-string
error-uri = "error_uri" = <"> URI-reference <">

The "scope" attribute is a space-delimited list of scope values
indicating the required scope of the access token for accessing the
requested resource. type specification.

7.1. Access Token Types

The "scope" attribute MUST NOT appear more than
once.

If the protected resource request included an access token and failed
authentication, the resource server SHOULD include the "error"
attribute to provide type provides the client with the reason why the access
request was declined. The parameter value is described in
Section 6.2.1. In addition, the resource server MAY include the
"error_description" attribute information
required to provide a human-readable
explanation, and the "error-uri" attribute with an absolute URI
identifying a human-readable web page explaining successfully utilize the error. The
"error", "error_description", and "error_uri" attribute MUST NOT
appear more than once.

For example, in response to a protected resource request without
authentication:

HTTP/1.1 401 Unauthorized
WWW-Authenticate: OAuth2

And in response access token to make a protected
resource request (along with an
authentication attempt using an expired access token:

HTTP/1.1 401 Unauthorized
WWW-Authenticate: OAuth2
error="invalid_token",
error_description="The access type-specific attributes).

For example, the "bearer" token expired"

6.2.1. Error Codes

When a request fails, type defined in
[I-D.ietf-oauth-v2-bearer] is utilized by simply including the resource server responds using access
token string in the
appropriate HTTP status code (typically, 400, 401, or 403), and
includes one of request:

GET /resource/1 HTTP/1.1
Host: example.com
Authorization: BEARER h480djs93hd8

while the following error codes "mac" token type defined in the response:

invalid_request
The request [I-D.hammer-oauth-v2-mac-token]
is missing utilized by issuing a required parameter, includes an
unsupported parameter or parameter value, repeats token secret together with the same
parameter, uses more than one method for including an access
token, or token
which is otherwise malformed. The resource server SHOULD
respond with used to sign certain components of the HTTP 400 (Bad Request) status code.

invalid_token
The requests:

GET /resource/1 HTTP/1.1
Host: example.com
Authorization: MAC token="h480djs93hd8",
timestamp="137131200",
nonce="dj83hs9s",
signature="kDZvddkndxvhGRXZhvuDjEWhGeE="

Each access token provided is expired, revoked, malformed, or
invalid for other reasons. The resource SHOULD respond type definition specifies the additional attributes
(if any) sent to the client together with the "access_token" response
parameter. It also defines the HTTP 401 (Unauthorized) status code. The client MAY
request a new authentication method used to
include the access token and retry the when making a protected resource request.

insufficient_scope
The request requires higher privileges than provided by

8. Extensibility

8.1. Defining Access Token Types

Access token types can be defined in one of two ways: registered in
the access token. The token type registry (following the procedures in
Section 10.1), or use the "x_" type name prefix.

Types utilizing the "x_" name prefix MUST be limited to vendor-
specific implementations that are not commonly applicable, and are
specific to the implementation details of the resource server SHOULD respond with where
they are used. If a vendor-specific type requires additional vendor-
specific token response parameters, they MUST also use the HTTP
403 (Forbidden) status code "x_" name
prefix.

All other types MUST be registered, and MAY include the "scope"
attribute with MUST NOT use the scope necessary "x_" type
name prefix. Type names MUST conform to access the protected
resource.

[[ Add mechanism for extending error codes ]] type-name ABNF. If the request lacks any authentication information (i.e. the client
was unaware authentication is necessary or attempted using an
unsupported
type definition includes a new HTTP authentication method), scheme, the resource server type
name SHOULD not
include an error code or other error information.

For example:

HTTP/1.1 401 Unauthorized
WWW-Authenticate: OAuth2

7. Extensibility

7.1. Defining New Client Credentials Types

[[ TBD ]]

7.2. be identical to the authentication scheme name (as
defined by [RFC2617]).

type-name = 1*name-char
name-char = "-" / "." / "_" / DIGIT / ALPHA

8.2. Defining New Endpoint Parameters

Applications that wish to define new

New request or response parameters for use with the end-user authorization
endpoint or the token endpoint SHALL do so can be added in one of two ways: register them
registered in the parameters registry (following the procedures in
Section 9.1), 10.2), or use the "x_" parameter name prefix.

Parameters utilizing the "x_" parameter name prefix MUST be limited
to vendor-specific extensions that are not commonly applicable, and
are specific to the implementation details of the authorization
server where they are used. All other new parameters MUST be
registered, and MUST NOT use the "x_" parameter name prefix.

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).

param-name = 1*name-char
name-char = "-" / "." / "_" / DIGIT / ALPHA

7.3.

8.3. Defining New Header Field Parameters

Applications that wish to define new parameters Authorization Grant Types

New authorization grant types can be defined by assigning them a
unique URI for use in with the OAuth
"WWW-Authenticate" header field "grant_type" parameter. If the extension
grant type requires additional token endpoint parameters, they MUST register them
be registered in the OAuth parameters
registry, following the procedures in registry as described by
Section 9.1.

Parameter names MUST conform to 10.2.

9. Security Considerations

[[ TBD ]]

10. IANA Considerations

10.1. The OAuth Access Token Type Registry

This specification establishes the param-name ABNF and MUST NOT
begin OAuth access token type registry.

Access token types are registered on the advice of one or more
Designated Experts (appointed by the IESG or their delegate), with "x_". Parameter a
Specification Required (using terminology from [RFC5226]). However,
to allow for the allocation of values MUST conform prior to publication, the param-value
ABNF and their syntax MUST
Designated Expert(s) may approve registration once they are satisfied
that such a specification will be well-defined published.

Registration requests should be sent to the [TBD]@ietf.org mailing
list for review and comment, with an appropriate subject (e.g., using ABNF, or a
reference
"Request for access toke type: example"). [[ Note to RFC-EDITOR: The
name of the syntax mailing list should be determined in consultation with
the IESG and IANA. Suggested name: oauth-ext-review. ]]

param-value = quoted-value | quoted-string

7.4. Defining explanation and, if applicable, suggestions as to how to make the
request successful. Registration requests that are undetermined for
a period longer than 21 days can be brought to the IESG's attention
(using the iesg@iesg.org mailing list) for resolution.

10.1.1. Registration Template

Type name:
The name requested (e.g., "example").
Additional Token Endpoint Response Parameters:
Additional response parameters returned together with the
"access_token" parameter. New Access Grant Types parameters MUST be separately
registered in the OAuth parameters registry as described by
Section 10.2.
HTTP Authentication Scheme(s):
The assertion HTTP authentication scheme name(s), if any, used to
authenticate protected resources requests using access grant type allows token of
this type.
Change controller:
For standards-track RFCs, state "IETF". For others, give the authorization server name
of the responsible party. Other details (e.g., postal address,
e-mail address, home page URI) may also be included.

Specification document(s):
Reference to
accept additional access grants not specified. Applications document that specifies the parameter, preferably
including a URI that
wish to define additional access grant types can do so by utilizing be used to retrieve a
new or existing assertion type and format.

8. Security Considerations

[[ TBD ]]

9. IANA Considerations

9.1. copy of the
document. An indication of the relevant sections may also be
included, but is not required.

10.2. The OAuth Parameters Registry

This document specification establishes the OAuth parameters registry.

Additional parameters to be use for inclusion in the end-user authorization endpoint
request, the end-user authorization endpoint response, the token endpoint
request, or the token endpoint response, or the
"WWW-Authenticate" header field, are registered on the advice
of one or more Designated Experts (appointed by the IESG or their
delegate), with a Specification Required (using terminology from
[RFC5226]). However, to allow for the allocation of values prior to
publication, the Designated Expert(s) may approve registration once
they are satisfied that such a specification will be published.

Registration requests should be sent to the [TBD]@ietf.org mailing
list for review and comment, with an appropriate subject (e.g.,
"Request for parameter: example"). [[ Note to RFC-EDITOR: The name of
the mailing list should be determined in consultation with the IESG
and IANA. Suggested name: oauth-ext-review. ]]

Before a period of 14 days has passed, the Designated Expert(s) will
either approve or deny the registration request, communicating this
decision both to the review list and to IANA. Denials should include
an explanation and, if applicable, suggestions as to how to make the
request successful. Registration requests that are undetermined for
a period longer than 21 days can be brought to the IESG's attention
(using the iesg@iesg.org mailing list) for resolution.

9.1.1.

10.2.1. Registration Template

Parameter name:
The name requested (e.g., "example").
Parameter usage location:
The location(s) where parameter can be used. The possible
locations are: the end-user authorization
endpoint request, the end-user authorization endpoint response,
the
token endpoint request, the token endpoint response, the or
the "WWW-Authenticate" header field. token response.
Change controller:
For standards-track RFCs, state "IETF". For others, give the name
of the responsible party. Other details (e.g., postal address,
e-mail address, home page URI) may also be included.

Specification document(s):
Reference to document that specifies the parameter, preferably
including a URI that can be used to retrieve a copy of the
document. An indication of the relevant sections may also be
included, but is not required.

Related information: Optionally, citations to additional documents
containing further relevant information.

9.1.2. Example

10.2.2. Initial Registry Contents

The following is the parameter registration OAuth Parameters Registry's initial contents are:

o Parameter name: client_id
o Parameter usage location: authorization request, token request for the "scope"
parameter as defined in
o Change controller: IETF
o Specification document(s): [[ this document ]]

o Parameter name: client_secret
o Parameter usage location: token request
o Change controller: IETF
o Specification document(s): [[ this document ]]

o Parameter name: response_type
o Parameter usage location: authorization request
o Change controller: IETF
o Specification document(s): [[ this document ]]

o Parameter name: redirect_uri
o Parameter usage location: authorization request, token request
o Change controller: IETF
o Specification document(s): [[ this specification: document ]]

o Parameter name: scope
o Parameter usage location: The end-user authorization endpoint request, the end-user authorization endpoint
response, the token
endpoint request, the token endpoint response
o Change controller: IETF
o Specification document(s): [[ this document ]]

o Parameter name: state
o Parameter usage location: authorization request, authorization
response
o Change controller: IETF
o Specification document(s): [[ this document ]]

o Parameter name: code
o Parameter usage location: authorization response, and the
"WWW-Authenticate" header field. token request
o Change controller: IETF
o Specification document(s): [[ this document ]]
o Parameter name: error_description
o Parameter usage location: authorization response, token response
o Change controller: IETF
o Specification document(s): [[ this document ]]

o Parameter name: error_uri
o Parameter usage location: authorization response, token response
o Change controller: IETF
o Specification document(s): [[ this document ]]

o Parameter name: grant_type
o Parameter usage location: token request
o Change controller: IETF
o Specification document(s): [[ this document ]]

o Parameter name: access_token
o Parameter usage location: authorization response, token response
o Change controller: IETF
o Specification document(s): [[ this document ]]

o Parameter name: token_type
o Parameter usage location: authorization response, token response
o Change controller: IETF
o Specification document(s): [[ this document ]]

o Parameter name: expires_in
o Parameter usage location: authorization response, token response
o Change controller: IETF
o Specification document(s): [[ this document ]]

o Parameter name: username
o Parameter usage location: token request
o Change controller: IETF
o Specification document(s): [[ this document ]]

o Parameter name: password
o Parameter usage location: token request
o Change controller: IETF
o Specification document(s): [[ this document ]]

o Parameter name: refresh_token
o Parameter usage location: token request, token response
o Change controller: IETF
o Specification document(s): [[ this document ]]

Related information: None

Appendix A. Examples

[[ TBD ]]

Appendix B. Contributors

The following people contributed to preliminary versions of this
document: Blaine Cook (BT), Brian Eaton (Google), Yaron Goland
(Microsoft), Brent Goldman (Facebook), Raffi Krikorian (Twitter),
Luke Shepard (Facebook), and Allen Tom (Yahoo!). The content and
concepts within are a product of the OAuth community, WRAP community,
and the OAuth Working Group.

The OAuth Working Group has dozens of very active contributors who
proposed ideas and wording for this document, including: [[ If your
name is missing or you think someone should be added here, please
send Eran a note - don't be shy ]]

Michael Adams, Andrew Arnott, Dirk Balfanz, Brian Campbell, Leah
Culver, Bill de hOra, Brian Ellin, Igor Faynberg, George Fletcher,
Tim Freeman, Evan Gilbert, Kristoffer Gronowski, Justin Hart, Phil
Hunt, Mike Jones, John Kemp, Chasen Le Hara, Torsten Lodderstedt,
Alastair Mair, Eve Maler, James Manger, Laurence Miao, Chuck
Mortimore, Justin Richer, Peter Saint-Andre, Nat Sakimura, Rob Sayre,
Marius Scurtescu, Naitik Shah, Justin Smith, Jeremy Suriel, Christian
Stuebner, Paul Tarjan, Franklin Tse, and Nick Walker.

Appendix C. Acknowledgements

[[ Add OAuth 1.0a authors + WG contributors ]]

Appendix D. Document History

[[ to be removed by RFC editor before publication as an RFC ]]

-12

o Complete restructure with lots of new prose.
o Removed terminology and expanded terms in overview.
o Changed assertions to extensions and added informative reference
to the SAML 2.0 extension.
o Renamed access grant to authorization grant.
o Clarified 'token_type' as case insensitive.
o Authorization endpoint requires TLS when an access token is
issued.

o Removed client assertion credentials, mandatory HTTP Basic
authentication support for client credentials, WWW-Authenticate
header, and the OAuth2 authentication scheme.
o Changed implicit grant (aka user-agent flow) error response from
query to fragment.
o Removed the 'redirect_uri_mismatch' error code since in such a
case, the authorization server must not send the error back to the
client.
o Added parameter registration for all parameters in this
specification.
o Defined access token type registry.

-11

o Many editorial changes. Fixed user authorization section
structure. Removed unused normative references. Adjusted
language regarding single use of authorization codes.
o Fixed header ABNF.
o Change access token description from shared symmetric secret to
password.
o Moved access grant 'none' to a separate section, renamed to
'client_credentials'.
o Demoted the HTTP status code requirement from MUST to SHOULD in
protected resource response error.
o Removed 'expired_token' error code.
o Moved all the 'code_and_token' parameter to the fragment (from
code being in the query).
o Removed 'assertion_type' parameter (moved to 'grant_type').
o Added note about redirecting to invalid redirection URIs (open
redirectors).
o Removed bearer token section, added new required 'token_type'
parameter with extensibility.
o 'error-uri' parameter value changed to absolute URI.
o OAuth 2.0 HTTP authentication scheme name changed to 'OAuth2'.
o Dropped the 'WWW-Authenticate' header field 'realm' parameter.
o Removed definition of access token characters.
o Added instructions for dealing with error and an invalid
redirection URI.

-10

o Fixed typos. Many editorial changes. Rewrote introduction.
removed terminology grouping.
o Allowed POST for end-user resource owner authorization endpoint.
o Fixed token endpoint to not require client authentication.
o Made URI query and POST body 'oauth_token' parameter optional.

o Moved all parameter names and values to use underscores.
o Changed 'basic_credentials' to 'password',
'invalid_client_credentials' and 'invalid_client_id' to
'invalid_client'.
o Added note that access token requests without an access grant
should not include a refresh token.
o Changed scheme name from 'Token' to 'OAuth', simplified request
format to simple string for token instead of key=value pair (still
supported for extensions).
o Defined permitted access token string characters (suitable for
inclusion in an HTTP header).
o Added a note about conflicts with previous versions.
o Moved 'client_id' definition from client authentication to access
token endpoint.
o Added definition for 'access grant'.

-09

o Fixed typos, editorial changes.
o Added token expiration example.
o Added scope parameter to end-user resource owner authorization endpoint
response.
o Added note about parameters with empty values (same as omitted).
o Changed parameter values to use '-' instead of '_'. Parameter
names still use '_'.
o Changed authorization endpoint client type to response type with
values: code, token, and both.
o Complete cleanup of error codes. Added support for error
description and URI.
o Add initial extensibility support.

-08

o Renamed verification code to authorization code.
o Revised terminology, structured section, added new terms.
o Changed flows to profiles and moved to introduction.
o Added support for access token rescoping.
o Cleaned up client credentials section.
o New introduction overview.
o Added error code for invalid username and password, and renamed
error code to be more consistent.
o Added access grant type parameter to token endpoint.

-07

o Major rewrite of entire document structure.

o Removed device profile.
o Added verification code support to user-agent flow.
o Removed multiple formats support, leaving JSON as the only format.
o Changed assertion "assertion_format" parameter to
"assertion_type".
o Removed "type" parameter from token endpoint.

-06

o Editorial changes, corrections, clarifications, etc.
o Removed conformance section.
o Moved authors section to contributors appendix.
o Added section on native applications.
o Changed error response to use the requested format. Added support
for HTTP "Accept" header.
o Flipped the order of the web server and user-agent flows.
o Renamed assertion flow "format" parameter name to
"assertion_format" to resolve conflict.
o Removed the term identifier from token definitions. Added a
cryptographic token definition.
o Added figure titles.
o Added server response 401 when client tried to authenticate using
multiple credentials.
o Clarified support for TLS alternatives, and added requirement for
TLS 1.2 support for token endpoint.
o Removed all signature and cryptography.
o Removed all discovery.
o Updated HTML4 reference.

-05

o Corrected device example.
o Added client credentials parameters to the assertion flow as
OPTIONAL.
o Added the ability to send client credentials using an HTTP
authentication scheme.
o Initial text for the "WWW-Authenticate" header (also added scope
support).
o Change authorization endpoint to end-user resource owner endpoint.
o In the device flow, change the "user_uri" parameter to
"verification_uri" to avoid confusion with the end-user resource owner
endpoint.
o Add "format" request parameter and support for XML and form-
encoded responses.

-04
o Changed all token endpoints to use "POST"
o Clarified the authorization server's ability to issue a new
refresh token when refreshing a token.
o Changed the flow categories to clarify the autonomous group.
o Changed client credentials language not to always be server-
issued.
o Added a "scope" response parameter.
o Fixed typos.
o Fixed broken document structure.

-03

o Fixed typo in JSON error examples.
o Fixed general typos.
o Moved all flows sections up one level.

-02

o Removed restriction on "redirect_uri" including a query.
o Added "scope" parameter.
o Initial proposal for a JSON-based token response format.

-01

o Editorial changes based on feedback from Brian Eaton, Bill Keenan,
and Chuck Mortimore.
o Changed device flow "type" parameter values and switch to use only
the token endpoint.

-00

o Initial draft based on a combination of WRAP and OAuth 1.0a.

10.

11. References

10.1.

11.1. Normative References

[I-D.ietf-httpbis-p1-messaging]
Fielding, R., Gettys, J., Mogul, J., Nielsen, H.,
Masinter, L., Leach, P., Berners-Lee, T., and J. Reschke,
"HTTP/1.1, part 1: URIs, Connections, and Message
Parsing", draft-ietf-httpbis-p1-messaging-09 (work in
progress), March 2010.

[RFC2045] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part One: Format of Internet Message
Bodies", RFC 2045, November 1996.

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.

[RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.

[RFC2617] Franks, J., Hallam-Baker, P., Hostetler, J., Lawrence, S.,
Leach, P., Luotonen, A., and L. Stewart, "HTTP
Authentication: Basic and Digest Access Authentication",
RFC 2617, June 1999.

[RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000.

[RFC2828] Shirey, R., "Internet Security Glossary", RFC 2828,
May 2000.

[RFC3023] Murata, M., St. Laurent, S., and D. Kohn, "XML Media
Types", RFC 3023, January 2001.

[RFC3447] Jonsson, J. and B. Kaliski, "Public-Key Cryptography
Standards (PKCS) #1: RSA Cryptography Specifications
Version 2.1", RFC 3447, February 2003.

[RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO
10646", STD 63, RFC 3629, November 2003.

[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, January 2005.

[RFC4627] Crockford, D., "The application/json Media Type for
JavaScript Object Notation (JSON)", RFC 4627, July 2006.

[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008.

[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246, August 2008.

[RFC5849] Hammer-Lahav, E., "The OAuth 1.0 Protocol", RFC 5849,
April 2010.

[W3C.REC-html401-19991224]
Raggett, D.,
Hors, A., Raggett, D., and I. Jacobs, "HTML 4.01
Specification", World Wide Web Consortium
Recommendation REC-html401-19991224, December 1999,
<http://www.w3.org/TR/1999/REC-html401-19991224>.

10.2.

11.2. Informative References

[I-D.hammer-oauth-v2-mac-token]
Hammer-Lahav, E., "HTTP Authentication: MAC
Authentication", draft-hammer-oauth-v2-mac-token-01 (work
in progress), January 2011.

[I-D.ietf-oauth-saml2-bearer]
Campbell, B. and C. Mortimore, "SAML 2.0 Bearer Assertion
Grant Type Profile for OAuth 2.0",
draft-ietf-oauth-saml2-bearer-00 (work in progress),
December 2010.

[I-D.ietf-oauth-v2-bearer]
Jones, M., Hardt, D., and D. Recordon, "The OAuth 2.0
Protocol: Bearer Tokens", draft-ietf-oauth-v2-bearer-01
(work in progress), December 2010.

[OASIS.saml-core-2.0-os]
Cantor, S., Kemp, J., Philpott, R., and E. Maler,
"Assertions and Protocol for the OASIS Security Assertion
Markup Language (SAML) V2.0", OASIS Standard saml-core-
2.0-os, March 2005.

Authors' Addresses

Eran Hammer-Lahav (editor)
Yahoo!

Email: eran@hueniverse.com
URI: http://hueniverse.com

David Recordon
Facebook

Email: davidrecordon@facebook.com dr@fb.com
URI: http://www.davidrecordon.com/
Dick Hardt
Microsoft

Email: dick.hardt@gmail.com
URI: http://dickhardt.org/