wdiff draft-mills-kitten-sasl-oauth-03.txt draft-mills-kitten-sasl-oauth-04.txt

KITTEN W. Mills
Internet-Draft T. Showalter
Intended status: Standards Track Yahoo! Inc.
Expires: January 2, May 3, 2012 H. Tschofenig
Nokia Siemens Networks
July 1,
October 31, 2011

Tunneled HTTP Authentication For

A SASL
draft-mills-kitten-sasl-oauth-03.txt

Abstract

Simple Authentication and Security Layer (SASL) is a framework GSS-API Mechanism for
providing authentication and data security services in connection-
oriented protocols via replaceable mechanisms. OAuth is a protocol
framework for delegated HTTP authentication and thereby provides
draft-mills-kitten-sasl-oauth-04.txt

Abstract

OAuth enables a
method for clients third-party application to obtain limited access to a
protected resource resource, either on behalf of a resource owner. owner by
orchestrating an approval interaction, or by allowing the third-party
application to obtain access on its own behalf.

This document defines the use of HTTP authentication how an application client uses OAuth over SASL, the
Simple Authentication and Security Layer (SASL) or the Generic
Security Service Application Program Interface (GSS-API) to access a
protected resource at a resource serve, and additionally defines
authorization and token issuing endpoint discovery. Thereby, it
enables schemes defined within the OAuth framework for non-HTTP-based
application protocols.

Clients typically store the user's long term credential. This does,
however, lead to significant security vulnerabilities, for example,
when such a credential leaks. A significant benefit of OAuth for
usage in those clients that usually
store passwords is storing tokens instead of passwords. This that the password is much
lower risk since tokens can be more replaced by a token.
Tokens typically provided limited in scope of access rights and can be managed
and revoked separately from the user user's long-term credential
(password).

Status of this Memo

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provisions of BCP 78 and BCP 79.

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This Internet-Draft will expire on January 2, May 3, 2012.

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Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6 7
3. The OAuth SASL Mechanism Specification . . . . . . . . . . . . . . . . . . . 7 8
3.1. Channel Binding . . . . . . . . . . . . . . . . . . . . . 7
3.1.1. Generating channel binding data to be exchanged . . . 7 8
3.2. Initial Client Response . . . . . . . . . . . . . . . . . 8
3.2.1. Query String in OAUTH-PLUS . . . . . . . . . . . . . . 8 9
3.3. Server's Response . . . . . . . . . . . . . . . . . . . . 9
3.3.1.
3.4. Mapping to SASL Identities . . . . . . . . . . . . . . 9
3.4. . . 10
3.5. Discovery Information . . . . . . . . . . . . . . . . . . 10
3.5.
3.6. Use of Signature Type Authorization . . . . . . . . . . . 11 12
4. Implementation Requirements . . . . . GSS-API OAuth Mechanism Specification . . . . . . . . . . . . 13 14
5. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 15
5.1. Successful Bearer Token Exchange . . . . . . . . . . . . . 14 15
5.2. MAC Authentication with Channel Binding . . . . . . . . . 14 15
5.3. Failed Exchange . . . . . . . . . . . . . . . . . . . . . 15 16
5.4. Failed Channel Binding . . . . . . . . . . . . . . . . . . 16 17
6. Security Considerations . . . . . . . . . . . . . . . . . . . 17 18
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18 19
7.1. SASL Registration . . . . . . . . . . . . . . . . . . . . 18 19
7.2. GSS-API Registration . . . . . . . . . . . . . . . . . . . 19
7.3. Link Type Registration . . . . . . . . . . . . . . . . . . 18
7.2.1. 19
7.3.1. OAuth 2 Authentication Endpoint . . . . . . . . . . . 18
7.2.2. 19
7.3.2. OAuth 2 Token Endpoint . . . . . . . . . . . . . . . . 19
7.2.3. 20
7.3.3. OAuth 1.0a Request Initiation Endpoint . . . . . . . . 19
7.2.4. 20
7.3.4. OAuth 1.0a Authorization Endpoint . . . . . . . . . . 19
7.2.5. 21
7.3.5. OAuth 1.0a Token Endpoint . . . . . . . . . . . . . . 20 21
8. Appendix A -- Document History . . . . . . . . . . . . . . . . 21 22
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 22 23
9.1. Normative References . . . . . . . . . . . . . . . . . . . 22 23
9.2. Informative References . . . . . . . . . . . . . . . . . . 23 24
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 24 25

1. Introduction

OAuth [I-D.ietf-oauth-v2] offers enables a standard mechanism for delegating
authentication typically used for the purpose of control third-party application to obtain
limited access to
resources. a protected resource, either on behalf of a
resource owner by orchestrating an approval interaction, or by
allowing the third-party application to obtain access on its own
behalf. The core OAuth specification defines a framework for
authentication [I-D.ietf-oauth-v2] does not
define the interaction between the client and token usage the resource server
with the access to a protected resource using an Access Token. This
functionality is described in two separate specifications, namely
[I-D.ietf-oauth-v2-bearer], and [I-D.ietf-oauth-v2-http-mac], whereby
the focus is on an HTTP-based environment. The
HTTP authorization schemes and tokens in this model are defined
separately, some are defined within environment only.

Figure 1 shows the OAuth 2 framework such abstract message flow as shown in Figure 1 of
[I-D.ietf-oauth-v2].

+--------+ +---------------+
| |--(A)- Authorization Request ->| Resource |
| | | Owner |
| |<-(B)-- Authorization Grant ---| |
| | +---------------+
| |
| | +---------------+
| |--(C)-- Authorization Grant -->| Authorization |
| Client | | Server |
| |<-(D)----- Access Token -------| |
| | +---------------+
| |
| | +---------------+
| |--(E)----- Access Token ------>| Resource |
| | | Server |
| |<-(F)--- Protected Resource ---| |
+--------+ +---------------+

Figure 1: Abstract OAuth 2.0 Protocol: Bearer Tokens [I-D.ietf-oauth-v2-bearer], and
some are free standing with OAuth 2 framework bindings such as MAC
Authentication [I-D.hammer-oauth-v2-mac-token] tokens. Protocol Flow

This
mechanism document takes advantage of the OAuth protocol and infrastructure its
deployment base to provide a way to use SASL [RFC4422] for as well as the
GSS-API [RFC2743] to gain access to resources for non-
HTTP-based protocols when using non-HTTP-
based protocols, such as IMAP the Internet Message Access Protocol (IMAP)
[RFC3501], which is what this memo uses in the examples.

The general authentication flow Simple Authentication and Security Layer (SASL) is that the application will first
obtain an access token from an OAuth token service a framework
for the resource.
Once the client has obtained an OAuth access token it then connects providing authentication and authenticated using this data security services in
connection-oriented protocols via replaceable mechanisms. It
provides a structured interface between protocols and mechanisms.
The resulting framework allows new protocols to reuse existing
mechanisms and allows old protocols to make use of new mechanisms.
The framework also provides a protocol for securing subsequent
protocol exchanges within a data security layer.

The Generic Security Service Application Program Interface (GSS-API)
[RFC2743] provides a framework for applications to support multiple
authentication mechanisms through a unified interface.

This document defines a SASL mechanism.

Figure 1 shows mechanism for OAuth, but it conforms to
the relationship new bridge between SASL and OAuth graphically.
Item (1) denotes the GSS-API called GS2 [RFC5801].
This means that this document defines both a SASL mechanism and a
GSS-API mechanism. Implementers may be interested in either the
SASL, the GSS-API, or even both mechanisms. To faciliate these two
variants, the description has been split into two parts, one part of
that provides normative references for those interested in the SASL
OAuth exchange mechanism (see Section 3), and a second part for those
implementers that remains
unchanged wish to implement the GSS-API portion (see
Section 4).

When OAuth is integrated into SASL and the GSS-API the high-level
steps are as follows:

(A) The client requests authorization from [I-D.ietf-oauth-v2], i.e. where the resource owner.
The authorization request can be made directly to the resource
owner (as shown), or preferably indirectly via the authorization
server as an intermediary.

(B) The client obtains and
refreshes Access Tokens. This document focuses receives an authorization grant which is a
credential representing the resource owner's authorization,
expressed using one of four grant types defined in this
specification or using an extension grant type. The authorization
grant type depends on item (2) where the
Access Token is presented method used by the client to request
authorization and the types supported by the authorization server.

(C) The client requests an access token by authenticating with the
authorization server and presenting the authorization grant.

(D) The authorization server authenticates the client and
validates the authorization grant, and if valid issues an access
token.

(E) The client requests the protected resource from the resource
server over SASL. and authenticates by presenting the access token.

(F) The resource server validates the access token, and if valid,
serves the request.

Steps (E) and (F) are not defined in [I-D.ietf-oauth-v2] and are the
main functionality specified within this document. Additionally, an
optional discovery exchange is defined. Consequently, the message
exchange shown in Figure 2 is the result of this specification. (1)
and (2) denote the optional discovery exchange steps that may happen
before the OAuth 2.0 protocol exchange messages in steps (A)-(D) are
executed. Steps (E) and (F) also defined in this specification.

----+
+--------+ +---------------+ |
| |--(C)-- |--(A)-- Authorization Request --->| Resource | |
| | | Owner | |Plain
| |<-(D)------ |<-(B)------ Access Grant ---------| | |OAuth
| | +---------------+ |2.0
| | |(1) |
| | Client Credentials & +---------------+ |
| |--(E)------ |--(C)------ Access Grant -------->| Authorization | |
| Client | | Server | |
| |<-(F)------ |<-(D)------ Access Token ---------| | |
| | (w/ Optional Refresh Token) +---------------+ |
| | ----+
| |
| | ----+
| | (Optional discovery) +---------------+ |
| |--(A)------- |--(1)------- User Name --------->| | |
| Client | | | |
| |<-(B)------ |<-(2)------ Authentication -------| | |
| | endpoint information | Resource | |OAuth
| | | Server | |over
| |--(G)------ |--(E)------ Access Token -------->| | |SASL
| |SASL/
| | | | |GSS-
| |<-(H)---- |<-(F)---- Protected Resource -----| | |(2) |API
+--------+ +---------------+ |
----+

Figure 1: Interworking 2: OAuth SASL Architecture

Note: The discovery procedure in OAuth is still work in progress.
Hence, the discovery components described in this document should
be considered incomplete and a tentative proposal. In general,
there is a trade off between a generic, externally available
defined discovery mechanisms (such as Webfinger using host-meta
[I-D.hammer-hostmeta])
[I-D.hammer-hostmeta], or [I-D.jones-simple-web-discovery]) and
configuration information exchanged in
band in-band between the protocol SASL
communication endpoints.

It is worthwhile to note that this specification is also compatible
with OAuth 1.0a [RFC5849].

2. Terminology

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

The reader is assumed to be familiar with the terms used in the OAuth
2.0 specification. specification [I-D.ietf-oauth-v2].

In examples, "C:" and "S:" indicate lines sent by the client and
server respectively. Line breaks have been inserted for readability.

Note that the IMAP SASL specification requires base64 encoding
message, not this memo.

3. The OAuth SASL Mechanism Specification

SASL is used as a generalized authentication method in a variety of
application layer protocols. This document defines the two SASL
mechanisms for usage with OAuth: "OAUTH" and "OAUTH-PLUS". The
"OAUTH" SASL mechanism to allow HTTP
Authorization schemes in the OAuth framework to be used within the provides bearer token alike semantic for SASL framework. In this model
while "OAUTH-PLUS" provides a client authenticates to an OAuth-
capable authorization server over HTTPS. This server then issues
tokens after successfully authenticating the resource owner.
Subsequently, the obtained token may be presented in an OAuth-
authenticated request semantic similar to the resource server. This mechanism further
provides compatibility with OAuth 1.0a [RFC5849] and the "OAuth" MAC
authentication scheme defined there. by utilizing a channel binding mechanism [RFC5056].

3.1. Channel Binding

[[TODO: make this -PLUS not -SSL since if you support CB you have to
support all types.]]

Channel binding [RFC5056] in this mechanism is defined in order to
allow satisfying the security requirements of the authorization
schemes used. This document defines the "OAUTH-PLUS" mechanism to
provide channel binding for the OAUTH mechanism.

If the specification for the underlying authorization scheme requires
a security layer layer, such as TLS [RFC5246] [RFC5246], the server SHOULD only provide
that scheme in offer
a mechanism with channel binding enabled.

3.1.1. Generating where channel binding data to can be exchanged enabled.

The channel binding data is computed by the client based on it's
choice of preferred channel binding type. As specified in [RFC5056] [RFC5056],
the channel binding information must MUST start with the channel binding
unique prefix prefix, followed by a colon (ASCII 0x3A), this is followed by a base64
encoded channel binding payload. The channel binding payload is the
raw data from the channel binding type if the raw channel binding
data is less than 500 bytes, if 500 bytes or larger bytes. If the raw channel binding payload data is 500
bytes or larger then a SHA-1 [RFC3174] hash of the raw channel
binding data.

3.1.1.1. Use cases of generating channel binding data is computed.

If the client is using tls-unique for a channel binding then the raw
channel binding data is equals the first TLS finished message. This is
under the 500 byte limit, so the channel binding payload sent to the
server would be the base64 encoded first TLS finished message.

In the case where the client has chosen tls-endpoint, the raw channel
binding data is the certificate of the server the client connected
to. This
to, which will frequently be 500 bytes or more, and if more. If it is then the
channel binding payload is the base64 encoded SHA-1 hash of the
server certificate.

3.2. Initial Client Response

The SASL client response is formatted as an HTTP [RFC2616] request.
The HTTP request is limited in that the path MUST be "/". In the
OAUTH mechanism no query string is allowed. The following header
lines are defined in the client response:

User (OPTIONAL): Contains the user identifier being
authenticated, and is provided to allow correct discovery
information to be returned.

Host (REQUIRED): Contains the host name to which the client
connected.

Authorization (REQUIRED): An HTTP Authorization header.. header.

The user name is provided by the client to allow the discovery
information to be customized for the user, a given server could allow
multiple authenticators and it needs to return the correct one. For
instance, a large ISP could provide mail service for several domains
who manage their own user information. For instance, users at foo-
example.com could be authenticated by an OAuth service at
https://oauth.foo-example.com/, and users at bar-example.com could be
authenticated by https://oauth.bar-example.com, but both could be
served by a hypothetical IMAP server running at a third domain,
imap.example.net.

3.2.1. Query String in OAUTH-PLUS

In the OAUTH-PLUS mechanism the channel binding information is
carried in the query string. OAUTH-PLUS defines following query
parameter(s):

cbdata (REQUIRED): Contains the base64 encoded channel binding
data, properly escaped as an HTML query parameter value.

3.3. Server's Response

The server validates the response per the specification for the
authorization scheme used. If the authorization scheme used includes
signing of the request parameters the client must provide a complete
HTTP style request that satisfies the data requirements for the
scheme in use.

In the OAUTH-PLUS mechanism the server examines the channel binding
data, extracts the channel binding unique prefix, and extracts the
raw channel biding data based on the channel binding type used. It
then computes it's own copy of the channel binding payload and
compares that to the payload sent by the client in the query
parameters of the tunneled HTTP request. Those two must be equal for
channel binding to succeed.

The server responds to a successful OAuth authentication successfully verified client message by
completing the SASL negotiation. The authentication scheme MUST
carry the user ID to be used as the authorization identity (identity
to act as). The server MUST use that ID as the user being
authorized, that is the user assertion we accept and not other
information such as from the URL or "User:" header.

The server responds to failed authentication by sending discovery
information in an HTTP style response with the HTTP status code set
to 401, and then failing the authentication.

If channel binding is in use and the channel binding fails the server
responds with a minimal HTTP response without discovery information
and the HTTP status code set to 412 to indicate that the channel
binding precondition failed. If the authentication scheme in use
does not include signing the server SHOULD revoke the presented
credential and the client SHOULD discard that credential.

3.3.1.

3.4. Mapping to SASL Identities

Some OAuth mechanisms can provide both an authorization identity and
an authentication identity. An example of this is OAuth 1.0a
[RFC5849] where the consumer key (oauth_consumer_key) identifies the
entity using to token which equates to the SASL authentication
identity, and is authenticated using the shared secret. The
authorization identity in the OAuth 1.0a case is carried in the token
(per the requirement above), which SHOULD validated independently.
The server MAY use a consumer key or other comparable identity in the
OAuth authorization scheme as the SASL authentication identity. If
an appropriate authentication identity is not available the server
MUST use the identity asserted in the token.

3.4.

3.5. Discovery Information

The server MUST send discovery information in response to a failed
authentication exchange or a request with an empty Authorization
header. If discovery information is returned it MUST include an
authentication endpoint appropriate for the user. If the "User"
header is present the discovery information MUST be for that user.
Discovery information is provided by the server to the client to
allow a client to discover the appropriate OAuth authentication and
token endpoints. The client then uses that information to obtain the
access token needed for OAuth authentication. The client SHOULD
cache and re-use the user specific discovery information for service
endpoints.

Discovery information makes use of both the WWW-Authenticate header
as defined in HTTP Authentication: Basic and Digest Access
Authentication [RFC2617] and Link headers as defined in [RFC5988].

The following elements are defined for discovery information:

WWW-Authenticate A WWW-Authenticate header for each authentication
scheme supported by the server. Authentication scheme names are
case insensitive. The following [RFC2617] authentication
parameters are defined:

realm REQUIRED -- (as defined by RFC2617)

scope OPTIONAL -- A quoted string. This provides the client an
OAuth 2 scope known to be valid for the resource.

oauth2-authenticator An [RFC5988] Link header specifying the
[I-D.ietf-oauth-v2] authentication endpoint. This link has an
OPTIONAL link-extension "scheme", if included this link applies
ONLY to the specified scheme.

oauth2-token An [RFC5988] Link header specifying the
[I-D.ietf-oauth-v2] token endpoint. This link has an OPTIONAL
link-extension "scheme", if included this link applies ONLY to the
specified scheme.

oauth-initiate (Optional) An [RFC5988] Link header specifying the
Oauth 1.0a
OAuth1.0a [RFC5849] initiation endpoint. The server MUST send
this if "OAuth" is included in the supported list of HTTP
authentication schemes for the server.

oauth-authorize (Optional) An [RFC5988] Link header specifying the
Oauth 1.0a
OAuth1.0a [RFC5849] authentication endpoint. The server MUST send
this if "OAuth" is included in the supported list of HTTP
authentication schemes for the server.

oauth-token (Optional) An [RFC5988] Link header specifying the Oauth
1.0a
OAuth1.0a [RFC5849] token endpoint. The server MUST send this if
"OAuth" is included in the supported list of HTTP authentication
schemes for the server. This link type has one link-extension
"grant-types" which is a space separated list of the the OAuth 2.0
grant types that can be used at the token endpoint to obtain a
token.

Usage of the URLs provided in the discovery information is defined in
the relevant specifications. If the server supports multiple
authenticators the discovery information returned for unknown users
MUST be consistent with the discovery information for known users to
prevent user enumeration. The OAuth 2.0 specification
[I-D.ietf-oauth-v2] supports multiple types of authentication schemes
and the server MUST specify at least one supported authentication
scheme in the discovery information. The server MAY support multiple
schemes and MAY support schemes not listed in the discovery
information.

If the resource server provides a scope the client SHOULD always
request scoped tokens from the token endpoint. The client MAY use a
scope other than the one provided by the resource server. Scopes
other than those advertised by the resource server must be defined by
the resource owner and provided in service documentation (which is
beyond the scope of this memo).

3.5.

3.6. Use of Signature Type Authorization

This mechanism supports authorization using signatures, which
requires that both client and server construct the string to be
signed. OAuth 2 is designed for authentication/authorization to
access specific URIs. SASL is designed for user authentication, and
has no facility for being more specific. In this mechanism we
require an HTTP style format specifically to support signature type
authentication, but this is extremely limited. The HTTP style
request is limited to a path of "/". This mechanism is in the SASL
model, but is designed so that no changes are needed if there is a
revision of SASL which supports more specific resource authorization,
e.g. IMAP access to a specific folder or FTP access limited to a
specific directory.

Using the example in the MAC specification
[I-D.hammer-oauth-v2-mac-token]
[I-D.ietf-oauth-v2-http-mac] as a starting point, on an IMAP server
running on port 143 and given the MAC style authorization request
(with long lines wrapped for readability) below:

GET / HTTP/1.1
Host: server.example.com
User: user@example.com
Authorization: MAC token="h480djs93hd8",timestamp="137131200",
nonce="dj83hs9s",signature="YTVjyNSujYs1WsDurFnvFi4JK6o="

The normalized request string would be constructed per the MAC
specifcation [I-D.hammer-oauth-v2-mac-token].
specification [I-D.ietf-oauth-v2-http-mac]. In this example the
normalized request string with the new line separator character is
represented by "\n" for display purposes only would be:

h480djs93hi8\n
137131200\n
dj83hs9s\n
\n
GET\n
server.example.com\n
143\n
/\n
\n

4. Implementation Requirements

Tokens typically have a restricted lifetime. In addition a
previously obtained token MAY be revoked or rendered invalid at any
time. GSS-API OAuth Mechanism Specification

Note: The client MAY request a new access token normative references in this section are informational for each connection
to a resource server,
SASL implementers, but it SHOULD cache they are normative for GSS-API implementers.

The SASL OAuth mechanism is also a GSS-API mechanism and re-use access
credentials that appear to be valid. Credential lifetime the messages
described in Section 3 are the same, but

1. the GS2 header on the client's first message is excluded when
OAUTH is used as a GSS-API mechanism, and how
that

2. initial context token header is communicated prefixed to the client is defined client's first
authentication message (context token), as described in Section
3.1 of RFC 2743,

The GSS-API mechanism OID for OAuth is [[TBD: IANA]].

OAuth security contexts always have the mutual_state flag
(GSS_C_MUTUAL_FLAG) set to TRUE. OAuth supports credential
delegation, therefore security contexts may have the deleg_state flag
(GSS_C_DELEG_FLAG) set to either TRUE or FALSE.

The mutual authentication
scheme specifications. Clients MAY implement any property of this mechanism relies on
successfully comparing the OAuth 2
profiles since they are largely outside TLS server identity with the scope negotiated
target name. Since the TLS channel is managed by the application
outside of the GSS-API mechanism, the mechanism itself is unable to
confirm the name while the application is able to perform this
specification, and
comparison for the mentioned profiles in mechanism. For this document reason, applications MUST
match the TLS server identity with the target name, as discussed in
[RFC6125].

The OAuth mechanism does not support per-message tokens or
GSS_Pseudo_random.

OAuth supports a standard generic name syntax for acceptors, such as
GSS_C_NT_HOSTBASED_SERVICE (see [RFC2743], Section 4.1). These
service names MUST be associated with the "entityID" claimed by the
RP. OAuth supports only a single name type for initiators:
GSS_C_NT_USER_NAME. GSS_C_NT_USER_NAME is the default name type.
The query, display, and exported name syntaxes for OAuth principal
names are just
examples. all the same. There is no OAuth-specific name syntax;
applications SHOULD use generic GSS-API name types, such as
GSS_C_NT_USER_NAME and GSS_C_NT_HOSTBASED_SERVICE (see [RFC2743],
Section 4). The exported name token does, of course, conform to
[RFC2743], Section 3.2, but the "NAME" part of the token should be
treated as a potential input string to the OAuth name normalization
rules.

5. Examples

These example illustrate exchanges between an IMAP client and an IMAP
server.

5.1. Successful Bearer Token Exchange

This example shows a successful OAuth 2.0 bearer token exchange with
an initial client response. Note that line breaks are inserted for
readability.

S: * IMAP4rev1 Server Ready
C: t0 CAPABILITY
S: * CAPABILITY IMAP4rev1 AUTH=OAUTH
S: t0 OK Completed
C: t1 AUTHENTICATE OAUTH R0VUIC8gSFRUUC8xLjENCkhvc3Q6IGltYXAuZXhhbXBs
ZS5jb20NCkF1dGhvcml6YXRpb246IEJFQVJFUiAidkY5ZGZ0NHFtVGMyTnZiM1J
sY2tCaGJIUmhkbWx6ZEdFdVkyOXRDZz09Ig0KDQo=
S: +
S: t1 OK SASL authentication succeeded

As required by IMAP [RFC3501], the payloads are base64-encoded. The
decoded initial client response is:

GET / HTTP/1.1
Host: imap.example.com
Authorization: BEARER "vF9dft4qmTc2Nvb3RlckBhbHRhdmlzdGEuY29tCg=="

The line containing just a "+" and a space is an empty response from
the server. This response contains discovery information, and in the
success case no discovery information is necessary so the response is
empty. Like other messages, and in accordance with the IMAP SASL
binding, the empty response is base64-encoded.

5.2. MAC Authentication with Channel Binding

This example shows a channel binding failure. The example sends the
same request as above, but in the context of an OAUTH-PLUS exchange
the channel binding information is missing. Note that line breaks
are inserted for readability.

S: * CAPABILITY IMAP4rev1 AUTH=OAUTH SASL-IR IMAP4rev1 Server Ready
S: t0 OK Completed
C: t1 AUTHENTICATE MAC R0VUIC8/Y2JkYXRhPSJTRzkzSUdKcFp5QnBjeUJoSUZSTVV5Q
m1hVzVoYkNCdFpYTnpZV2RsUHdvPSIgSFRUUC8xLjENCkhvc3Q6IHNlcnZlci5leGFtcG
xlLmNvbQ0KVXNlcjogdXNlckBleGFtcGxlLmNvbQ0KQXV0aG9yaXphdGlvbjogTUFDIHR
va2VuPSJoNDgwZGpzOTNoZDgiLHRpbWVzdGFtcD0iMTM3MTMxMjAwIixub25jZT0iZGo4
M2hzOXMiLHNpZ25hdHVyZT0iV1c5MUlHMTFjM1FnWW1VZ1ltOXlaV1F1SUFvPSINCg0K
S: +
S: t1 OK SASL authentication succeeded

As required by IMAP [RFC3501], the payloads are base64-encoded. The
decoded initial client response is:

GET /?cbdata="SG93IGJpZyBpcyBhIFRMUyBmaW5hbCBtZXNzYWdlPwo=" HTTP/1.1
Host: server.example.com
User: user@example.com
Authorization: MAC token="h480djs93hd8",timestamp="137131200",
nonce="dj83hs9s",signature="WW91IG11c3QgYmUgYm9yZWQuIAo="

The line conaining containing just a "+" and a space is an empty response from
the server. This response contains discovery information, and in the
success case no discovery information is necessary so the response is
empty. Like other messages, and in accordance with the IMAP SASL
binding, the empty response is base64-encoded.

5.3. Failed Exchange

This example shows a failed exchange because of the empty
Authorization header, which is how a client can query for discovery
information. Note that line breaks are inserted for readability.

S: * CAPABILITY IMAP4rev1 AUTH=OAUTH SASL-IR IMAP4rev1 Server Ready
S: t0 OK Completed
C: t1 AUTHENTICATE OAUTH R0VUIC8gSFRUUC8xLjENClVzZXI6IHNjb290ZXJAYW
x0YXZpc3RhLmNvbQ0KSG9zdDogaW1hcC55YWhvby5jb20NCkF1dGhlbnRpY2F0ZT
ogDQoNCg==
S: + SFRUUC8xLjEgNDAxIFVuYXV0aG9yaXplZA0KV1dXLUF1dGhlbnRpY2F0ZTogQk
VBUkVSIHJlYWxtPSJleGFtcGxlLmNvbSINCkxpbms6IDxodHRwczovL2xvZ2luLn
lhaG9vLmNvbS9vYXV0aD4gcmVsPSJvYXV0aDItYXV0aGVudGljYXRvciIgIA0KTG
luazogPGh0dHBzOi8vbG9naW4ueWFob28uY29tL29hdXRoPiByZWw9Im91YXRoMi
10b2tlbiINCg0K
S: t1 NO SASL authentication failed

The decoded initial client response is:

GET / HTTP/1.1
User: alice@example.com
Host: imap.example.com
Authorization:

The decoded server discovery response is:

HTTP/1.1 401 Unauthorized
WWW-Authenticate: BEARER realm="example.com"
Link: <https://login.example.com/oauth> rel="oauth2-authenticator"
Link: <https://login.example.com/oauth> rel="oauth2-token"

5.4. Failed Channel Binding

This example shows a channel binding failure in a discovery request.
The channel binding information is empty. Note that line breaks are
inserted for readability.

S: * CAPABILITY IMAP4rev1 AUTH=OAUTH SASL-IR IMAP4rev1 Server Ready
S: t0 OK Completed
C: t1 AUTHENTICATE OAUTH R0VUIC8/Y2JkYXRhPSIiIEhUVFAvMS4xDQpVc2VyOi
BhbGljZUBleGFtcGxlLmNvbQ0KSG9zdDogaW1hcC5leGFtcGxlLmNvbQ0KQXV0aG
9yaXphdGlvbjoNCg0K
S: + SFRUUC8xLjEgNDEyIFByZWNvbmRpdGlvbiBGYWlsZWQNCg0KDQo=
S: t1 NO SASL authentication failed

The decoded initial client response is:

GET /?cbdata="" HTTP/1.1
User: alice@example.com
Host: imap.example.com
Authorization:

The decoded server response is:

HTTP/1.1 412 Precondition Failed

6. Security Considerations

This mechanism does not provide a security layer, but does provide a
provision for channel binding. The OAuth 2 specification
[I-D.ietf-oauth-v2] allows for a variety of usages, and the security
properties of these profiles vary. The usage of bearer tokens, for
example, provide security features similar to cookies. Applications
using this mechanism SHOULD exercise the same level of care using
this mechanism as they would in using the SASL PLAIN mechanism. In
particular, TLS 1.2 or an equivalent secure channel MUST be
implemented and its usage is RECOMMENDED.

Channel binding in this mechanism has different properties based on
the authentication scheme used. Bearer tokens have the same
properties as cookies, and the bearer token authentication scheme has
no signature or message integrity. Channel binding to TLS with a bearer
token provides only a binding to the TLS layer. Authentication
schemes like MAC tokens have a signature over the channel binding
information. These provide additional protection against a man in
the middle, middle attacks, and the MAC authorization header is bound to the
channel and only valid in that context.

It is possible that SASL will be authenticating a connection and the
life of that connection may outlast the life of the token used to
authenticate it. This is a common problem in application protocols
where connections are long-lived, and not a problem with this
mechanism per se. Servers MAY unilaterally disconnect clients in
accordance with the application protocol.

An OAuth credential is not equivalent to the password or primary
account credential. There are protocols like XMPP that allow actions
like change password. The server SHOULD ensure that actions taken in
the authenticated channel are appropriate to the strength of the
presented credential.

It is possible for an application server running on Evil.example.com
to tell a client to request a token from Good.example.org. A client
following these instructions will pass a token from Good to Evil.
This is by design, since it is possible that Good and Evil are merely
names, not descriptive, and that this is an innocuous activity
between cooperating two servers in different domains. For instance,
a site might operate their authentication service in-house, but
outsource their mail systems to an external entity.

Tokens have a lifetime associated with them. Reducing both the
lifetime of a token provides security benefits in case that tokens
leak. In addition a previously obtained token MAY be revoked or
rendered invalid at any time. The client MAY request a new access
token for each connection to a resource server, but it SHOULD cache
and re-use access credentials that appear to be valid.

7. IANA Considerations

7.1. SASL Registration

The IANA is requested to register the following SASL profile:

SASL mechanism profile: OAUTH

Security Considerations: See this document

Published Specification: See this document

For further information: Contact the authors of this document.

Owner/Change controller: the IETF

Note: None

The IANA is requested to register the following SASL profile:

SASL mechanism profile: OAUTH-PLUS

Security Considerations: See this document

Published Specification: See this document

For further information: Contact the authors of this document.

Owner/Change controller: the IETF

Note: None

7.2. GSS-API Registration

IANA is further requested to assign an OID for this GSS mechanism in
the SMI numbers registry, with the prefix of
iso.org.dod.internet.security.mechanisms (1.3.6.1.5.5) and to
reference this specification in the registry.

7.3. Link Type Registration

Pursuant to [RFC5988] The following link type registrations [[will
be]] registered by mail to link-relations@ietf.org.

7.2.1.

7.3.1. OAuth 2 Authentication Endpoint
o Relation Name: oauth2-authenticator

o Description: An OAuth 2.0 authentication endpoint.

o Reference:

o Notes: This link type indicates an OAuth 2.0 authentication
endpoint that can be used for user authentication/authorization
for the endpoint providing the link.

o Application Data: [optional]

7.2.2.

7.3.2. OAuth 2 Token Endpoint

o Relation Name: oauth2-token

o Description: The OAuth token endpoint used to get tokens for
access.

o Reference:

o Notes: The OAuth 2.0 token endpoint to be used for obtaining
tokens to access the endpoint providing the link.

o Application Data: This link type has one link-extension "grant-
types"
types", which is the OAuth 2.0 grant types that can be used at the
token endpoint to obtain a token. This is not an exclusive list,
it provides a hint to the application of what SHOULD be valid. A
token endpoint MAY support additional grant types not advertised
by a resource endpoint.

7.2.3.

7.3.3. OAuth 1.0a Request Initiation Endpoint

o Relation Name: oauth-initiate

o Description: The OAuth 1.0a request initiation endpoint used to
get tokens for access.

o Reference:

o Notes: The OAuth 1.0a endpoint used to initiate the sequence, this
temporary request is what the user approves to grant access to the
resource.

o Application Data:

7.2.4.

7.3.4. OAuth 1.0a Authorization Endpoint

o Relation Name: oauth-authorize

o Description: The OAuth 1.0a authorization endpoint used to approve
an access request.

o Reference:

o Notes:

o Application Data:

7.2.5.

7.3.5. OAuth 1.0a Token Endpoint

o Relation Name: oauth-token

o Description: The OAuth 1.0a token endpoint used to get tokens for
access.

o Reference:

o Notes:

o Application Data:

8. Appendix A -- Document History

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

-04

o Editorial clean-up and text in introduction improved.

o Added GSS-API support

-03

o Fixing channel binding, not tls-unique specific. Also defining
how the CB data is properly generated.

o Various small editorial changes and embarassing spelling fixes.

-02

o Filling out Channel Binding

o Added text clarifying how to bind to the 2 kinds of SASL
identities.

-01

o Bringing this into line with draft 12 of the core spec, the bearer
token spec, and references the MAC token spec

o Changing discovery over to using the Link header construct from
RFC5988.

o Added the seeds of channel binding.

-00

o Initial revision

9. References

9.1. Normative References

[I-D.hammer-oauth-v2-mac-token]
Hammer-Lahav, E., "HTTP Authentication: MAC
Authentication", draft-hammer-oauth-v2-mac-token-02 (work
in progress), January 2011.

[I-D.ietf-oauth-v2]
Hammer-Lahav, E., Recordon, D., and D. Hardt, "The OAuth
2.0 Authorization Protocol", draft-ietf-oauth-v2-12 draft-ietf-oauth-v2-22 (work
in progress), January September 2011.

[I-D.ietf-oauth-v2-bearer]
Jones, M., Hardt, D., and D. Recordon, "The OAuth 2.0
Authorization Protocol: Bearer Tokens", draft-ietf-oauth-v2-bearer-02
draft-ietf-oauth-v2-bearer-13 (work in progress), January
October 2011.

[I-D.ietf-oauth-v2-http-mac]
Hammer-Lahav, E., Barth, A., and B. Adida, "HTTP
Authentication: MAC Access Authentication",
draft-ietf-oauth-v2-http-mac-00 (work in progress),
May 2011.

[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.

[RFC2743] Linn, J., "Generic Security Service Application Program
Interface Version 2, Update 1", RFC 2743, January 2000.

[RFC3174] Eastlake, D. and P. Jones, "US Secure Hash Algorithm 1
(SHA1)", RFC 3174, September 2001.

[RFC4422] Melnikov, A. and K. Zeilenga, "Simple Authentication and
Security Layer (SASL)", RFC 4422, June 2006.

[RFC5056] Williams, N., "On the Use of Channel Bindings to Secure
Channels", RFC 5056, November 2007.

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

[RFC5801] Josefsson, S. and N. Williams, "Using Generic Security
Service Application Program Interface (GSS-API) Mechanisms
in Simple Authentication and Security Layer (SASL): The
GS2 Mechanism Family", RFC 5801, July 2010.

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

[RFC5929] Altman, J., Williams, N., and L. Zhu, "Channel Bindings
for TLS", RFC 5929, July 2010.

[RFC5988] Nottingham, M., "Web Linking", RFC 5988, October 2010.

[RFC6125] Saint-Andre, P. and J. Hodges, "Representation and
Verification of Domain-Based Application Service Identity
within Internet Public Key Infrastructure Using X.509
(PKIX) Certificates in the Context of Transport Layer
Security (TLS)", RFC 6125, March 2011.

9.2. Informative References

[I-D.hammer-hostmeta]
Hammer-Lahav, E. and B. Cook, "Web Host Metadata",
draft-hammer-hostmeta-16
draft-hammer-hostmeta-17 (work in progress), May
September 2011.

[I-D.jones-simple-web-discovery]
Jones, M. and Y. Goland, "Simple Web Discovery (SWD)",
draft-jones-simple-web-discovery-01 (work in progress),
July 2011.

[RFC3501] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION
4rev1", RFC 3501, March 2003.

Authors' Addresses

William Mills
Yahoo! Inc.

Phone:
Email: wmills@yahoo-inc.com

Tim Showalter
Yahoo! Inc.

Phone:
Email: timshow@yahoo-inc.com

Hannes Tschofenig
Nokia Siemens Networks
Linnoitustie 6
Espoo 02600
Finland

Phone: +358 (50) 4871445
Email: Hannes.Tschofenig@gmx.net
URI: http://www.tschofenig.priv.at