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Versions: (draft-mills-kitten-sasl-oauth) 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23 RFC 7628

KITTEN                                                          W. Mills
Internet-Draft                                               Yahoo! Inc.
Intended status: Standards Track                            T. Showalter
Expires: March 5, 2013
                                                           H. Tschofenig
                                                  Nokia Siemens Networks
                                                       September 1, 2012


             A set of SASL and GSS-API Mechanisms for OAuth
                    draft-ietf-kitten-sasl-oauth-06

Abstract

   OAuth enables a third-party application to obtain limited access to 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.

   This document defines how an application client uses credentials
   obtained via OAuth over 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.
   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 is that the password is replaced by a token.
   Tokens typically provided limited access rights and can be managed
   and revoked separately from the user's long-term credential
   (password).

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."



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   This Internet-Draft will expire on March 5, 2013.

Copyright Notice

   Copyright (c) 2012 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.



































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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  7
   3.  OAuth SASL Mechanism Specifications  . . . . . . . . . . . . .  8
     3.1.  Initial Client Response  . . . . . . . . . . . . . . . . .  9
       3.1.1.  Reserved Key/Values  . . . . . . . . . . . . . . . . . 10
       3.1.2.  Use of the gs2-header  . . . . . . . . . . . . . . . . 10
     3.2.  Server's Response  . . . . . . . . . . . . . . . . . . . . 10
       3.2.1.  Mapping to SASL Identities . . . . . . . . . . . . . . 11
       3.2.2.  Canonicalization . . . . . . . . . . . . . . . . . . . 11
       3.2.3.  Server response to failed authentication.  . . . . . . 11
       3.2.4.  Completing an error message sequence.  . . . . . . . . 12
     3.3.  Use of Signature Type Authorization  . . . . . . . . . . . 12
     3.4.  Channel Binding  . . . . . . . . . . . . . . . . . . . . . 13
   4.  GSS-API OAuth Mechanism Specification  . . . . . . . . . . . . 14
   5.  Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
     5.1.  Successful Bearer Token Exchange . . . . . . . . . . . . . 16
     5.2.  OAuth 1.0a Authorization with Channel Binding  . . . . . . 17
     5.3.  Failed Exchange  . . . . . . . . . . . . . . . . . . . . . 18
     5.4.  Failed Channel Binding . . . . . . . . . . . . . . . . . . 19
     5.5.  SMTP Example of a failed negotiation.  . . . . . . . . . . 19
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . . 21
   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 22
     7.1.  SASL Registration  . . . . . . . . . . . . . . . . . . . . 22
     7.2.  GSS-API Registration . . . . . . . . . . . . . . . . . . . 23
   8.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 24
     8.1.  Normative References . . . . . . . . . . . . . . . . . . . 24
     8.2.  Informative References . . . . . . . . . . . . . . . . . . 25
   Appendix A.  Acknowlegements . . . . . . . . . . . . . . . . . . . 26
   Appendix B.  Document History  . . . . . . . . . . . . . . . . . . 27
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 29



















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1.  Introduction

   OAuth [I-D.ietf-oauth-v2] enables a third-party application to obtain
   limited access to 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 [I-D.ietf-oauth-v2] does not
   define the interaction between the client and the resource server
   with the access to a protected resource using an Access Token.  This
   functionality is described in separate specifications, for example
   Bearer tokens [I-D.ietf-oauth-v2-bearer], MAC tokens
   [I-D.ietf-oauth-v2-http-mac], and OAuth 1.0a [RFC5849].  In each of
   these are defined in an HTTP-based environment only.

   Figure 1 shows the 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 -------|               |
        |        |                               +---------------+
        |        |
        |        |                               +---h------------+
        |        |--(E)----- Access Token ------>|    Resource   |
        |        |                               |     Server    |
        |        |<-(F)--- Protected Resource ---|               |
        +--------+                               +---------------+

                Figure 1: Abstract OAuth 2.0 Protocol Flow

   This document takes advantage of the OAuth protocol and its
   deployment base to provide a way to use SASL [RFC4422] as well as the
   GSS-API [RFC2743] to gain access to resources when using non-HTTP-
   based protocols, such as the Internet Message Access Protocol (IMAP)
   [RFC3501] and SMTP [RFC5321], which is what this memo uses in the
   examples.

   The Simple Authentication and Security Layer (SASL) is a framework
   for providing authentication and data security services in
   connection-oriented protocols via replaceable mechanisms.  It



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   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 SASL mechanisms for OAuth, and it conforms to
   the new bridge between SASL and the GSS-API called GS2 [RFC5801].
   This means that this document defines both SASL and GSS-API
   mechanisms.  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 that provides
   normative references for those interested in the SASL OAuth mechanism
   (see Section 3), and a second part for those implementers that 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 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 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 the 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 and authenticates by presenting the access token.

      (F) The resource server validates the access token, and if valid,
      indicates a successful authentication.




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   Steps (E) and (F) are not defined in [I-D.ietf-oauth-v2] and are the
   main functionality specified within this document.  Consequently, the
   message exchange shown in Figure 2 is the result of this
   specification.  The client will genrally need to determine the
   authentication endpoints (and perhaps the service endpoints) before
   the OAuth 2.0 protocol exchange messages in steps (A)-(D) are
   executed.  The discovery of the resource owner and authorization
   server endpoints is outside the scope of this specification.  The
   client must discover those endpoints using a discovery mechanisms
   such as Webfinger using host-meta [I-D.jones-appsawg-webfinger].  In
   band discovery is not tenable if clients support the OAuth 2.0
   password grant.  Once credentials are obtained the client proceeds to
   steps (E) and (F) defined in this specification.


                                                              ----+
   +--------+                                  +---------------+  |
   |        |--(A)-- Authorization Request --->|   Resource    |  |
   |        |                                  |     Owner     |  |Plain
   |        |<-(B)------ Access Grant ---------|               |  |OAuth
   |        |                                  +---------------+  |2.0
   |        |                                                     |
   |        |         Client Credentials &     +---------------+  |
   |        |--(C)------ Access Grant -------->| Authorization |  |
   | Client |                                  |     Server    |  |
   |        |<-(D)------ Access Token ---------|               |  |
   |        |      (w/ Optional Refresh Token) +---------------+  |
   |        |                                                 ----+
   |        |                                                 ----+
   |        |                                  +---------------+  |
   |        |                                  |               |  |OAuth
   |        |--(E)------ Access Token -------->|    Resource   |  |over
   |        |                                  |     Server    |  |SASL/
   |        |<-(F)---- Protected Resource -----|               |  |GSS-
   |        |                                  |               |  |API
   +--------+                                  +---------------+  |
                                                              ----+

                     Figure 2: OAuth SASL Architecture












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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 [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.





































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3.  OAuth SASL Mechanism Specifications

   SASL is used as a generalized authentication method in a variety of
   application layer protocols.  This document defines the following
   SASL mechanisms for usage with OAuth:



      OAUTHBEARER  Authorization using Bearer tokens.

      OAUTH10A  Authorization using OAuth 1.0a tokens.

      OAUTH10A-PLUS  Adds channel binding [RFC5056] capability to
         OAUTH10A for additional security guarantees.

   Any new OAuth token scheme MAY define a new SASL mechanism compatible
   with the mechanisms defined here by simply registering the new
   name(s) and citing this specification for the further definition.
   New channel binding enabled "-PLUS" mechanisms defined in this way
   MUST include message integrity protection.  A newly defined mechanism
   would also need to register a new GS2 OID.

   These mechanisms are client initiated and lock-step, the server
   always replying to a client message.  In the case where the client
   has and correctly uses a valid token the flow is:

   o  Client sends a valid and correct initial client response.

   o  Server responds with a successful authentication.

   In the case where authorization fails the server sends an error
   result, then client MUST then send an additional message to the
   server in order to allow the server to finish the exchange.  Some
   protocols and common SASL implementations do not support both sending
   a SASL message and finalizing a SASL negotiation, the additional
   client message in the error case deals with this problem.  This
   exchange is:

   o  Client sends an invalid initial client response.

   o  Server responds with an error message.

   o  Client sends an empty client reponse.

   o  Server fails the authentication.






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3.1.  Initial Client Response

   Client responses are a key/value pair sequence.  The initial client
   response includes a gs2-header as defined in GS2 [RFC5801], which
   carries the authorization ID.  These key/value pairs carry the
   equivalent values from an HTTP context in order to be able to
   complete an OAuth style HTTP authorization.  The client MUST send an
   authorization ID in the gs2-header.  The ABNF [RFC5234] syntax is:



     kvsep          = %x01
     key            = 1*ALPHA
     value          = *(VCHAR | SP | HTAB | CR | LF )
     kvpair         = key "=" value kvsep
     client_resp    = 0*kvpair kvsep
     ;; gs2-header  = As defined in GSS-API
     initial_client_resp = gs2-header kvsep client_resp

   The following key/value pairs are defined in the client response:



      auth (REQUIRED):  The payload of the HTTP Authorization header for
         an equivalent HTTP OAuth authroization.

      host:  Contains the host name to which the client connected.

      port:  Contains the port number represented as a decimal positive
         integer string without leading zeros to which the client
         connected.

      qs:  The HTTP query string.  In non-channel binding mechanisms
         this is reserved, the client SHOUD NOT send it, and has the
         default value of "".  In "-PLUS" variants this carries a single
         key value pair "cbdata" for the channel binding data payload
         formatted as an HTTP query string.

   In authorization schemes that use signatures, the client MUST send
   host and port number key/values, and the server MUST fail an
   authorization request requiring signatures that does not have host
   and port values.  For authorization schemes that require a URI scheme
   as part of the data being signed "http" is always used.  In OAuth
   1.0a for example, the signature base string includes the
   reconstructed HTTP URL.






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3.1.1.  Reserved Key/Values

   In these mechanisms values for path, query string and post body are
   assigned default values.  OAuth authorization schemes MAY define
   usage of these in the SASL context and extend this specification.
   For OAuth schemes that use request signatures the default values MUST
   be used unless explict values are provided in the client response.
   The following key values are reserved for future use:



      mthd (RESERVED):  HTTP method for use in signatures, the default
         value is "POST".

      path (RESERVED):  HTTP path data, the default value is "/".

      post (RESERVED):  HTTP post data, the default value is "".

3.1.2.  Use of the gs2-header

   The OAuth scheme related mechanisms are also GSS-API mechanisms, see
   Section 4 for further detail.  The gs2-header is used as follows:

   o  The "gs2-nonstd-flag" MUST NOT be present.

   o  The "gs2-authzid" carries the authorization identity as specified
      in [RFC5801].  This MUST agree with the identity asserted in the
      OAuth credential.

   In the non "-PLUS" mechanisms the "gs2-cb-flag" MUST be set to "n"
   because channel-binding [RFC5056] data is not expected.  In the
   OAUTH10A-PLUS mechanism (or other -PLUS variants based on this
   specification) the "gs2-cb-flag" MUST be set appropriately by the
   client.

3.2.  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 client
   response that satisfies the data requirements for the scheme in use.

   In a "-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 cbdata key/value.
   Those two must be equal for channel binding to succeed.



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   The server responds to a successfully verified client message by
   completing the SASL negotiation.  The authorization scheme MUST carry
   the user ID to be used as the authorization identity (identity to act
   as).  The server MUST use the ID obtained from the credential as the
   user being authorized.

3.2.1.  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 the token which equates to the SASL authentication
   identity, and is authenticated using the shared secret.  The server
   MAY use a consumer key, a value derived from it, or other comparable
   identity in the OAuth authorization scheme to allow SASL an
   authentication identity different from the authorization identity to
   be set.

3.2.2.  Canonicalization

   The identity asserted by the OAuth authorization server is canonical
   for display.  The server MAY provide a different canonical form based
   on local data.

3.2.3.  Server response to failed authentication.

   For a failed authentication the server returns a JSON [RFC4627]
   formatted error result, and fails the authentication.  The error
   result consists of the following values:



      status (REQUIRED):  The authorization error code.  Valid error
         codes are defined in the IANA [[need registry name]] registry
         specified in the OAuth 2 core specification.

      scope (OPTIONAL):  An OAuth scope which is valid to access the
         service.  This may be empty which implies that unscoped tokens
         are required, or a space separated list.  Use of a space
         separated list is NOT RECOMMENDED.

   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 are be defined by
   the resource owner and provided in service documentation or discovery
   information (which is beyond the scope of this memo).  If not present
   then the client SHOULD presume an empty scope (unscoped token) is



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   needed.

   If channel binding is in use and the channel binding fails the server
   responds with a 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.

3.2.4.  Completing an error message sequence.

   Section 3.6 of [RFC4422] explicitly prohibits additional information
   in an unsuccessful authentication outcome.  Therefor, the error
   message is sent in a normal message.  The client MUST then send an
   additional client response consisting of a single %x01 (control A)
   character to the server in order to allow the server to finish the
   exchange.

3.3.  Use of Signature Type Authorization

   Some OAuth mechanisms support 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 or define default values for the data elements from an HTTP
   request which allow the signature base string to be constructed
   properly.  The default HTTP path is "/" and the default post body is
   empty.  These atoms are defined as extension points 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 OAuth 1.0a specification as a starting
   point, on an IMAP server running on port 143 and given the OAuth 1.0a
   style authorization request (with %x01 shown as ^A and line breaks
   added for readability) below:


   n,a=user@example.com^A
   host=example.com^A
   user=user@example.com^A
   port=143^A
   auth=OAuth realm="Example",
              oauth_consumer_key="9djdj82h48djs9d2",
              oauth_token="kkk9d7dh3k39sjv7",
              oauth_signature_method="HMAC-SHA1",
              oauth_timestamp="137131201",
              oauth_nonce="7d8f3e4a",



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              oauth_signature="Tm90IGEgcmVhbCBzaWduYXR1cmU%3D"^A^A

   The signature base string would be constructed per the OAuth 1.0
   specification [RFC5849] with the following things noted:

   o  The method value is defaulted to POST.

   o  The scheme defaults to be "http", and any port number other than
      80 is included.

   o  The path defaults to "/".

   o  The query string defaults to "".

   In this example the signature base string with line breaks added for
   readability would be:


   POST&http%3A%2F%2Fexample.com:143%2F&oauth_consumer_key%3D9djdj82h4
   8djs9d2%26oauth_nonce%3D7d8f3e4a%26oauth_signature_method%3DHMAC-SH
   A1%26oauth_timestamp%3D137131201%26oauth_token%3Dkkk9d7dh3k39sjv7

3.4.  Channel Binding

   The channel binding data is carried in the "qs" (query string) key
   value pair formatted as a standard HTTP query parameter with the name
   "cbdata".  Channel binding requires that the channel binding data be
   integrity protected end-to-end in order to protect against man-in-
   the-middle attacks.  All authorization schemes offered with "-PLUS"
   mechanisms MUST provide integrity protection.  It should be noted
   that while the Bearer token scheme specifies SSL for normal usage it
   offers no integrity protection and is not suitable for use with
   channel binding.

   The channel binding data is computed by the client based on it's
   choice of preferred channel binding type.  As specified in [RFC5056],
   the channel binding information MUST start with the channel binding
   unique prefix, followed by a colon (ASCII 0x3A), followed by a base64
   encoded channel binding payload.  The channel binding payload is the
   raw data from the channel binding type.  For example, if the client
   is using tls-unique for channel binding then the raw channel binding
   data is the TLS finished message as specified in section 3.1 of
   [RFC5929].








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4.  GSS-API OAuth Mechanism Specification

   Note: The normative references in this section are informational for
   SASL implementers, but they are normative for GSS-API implementers.

   A SASL OAuth mechanism is also a GSS-API mechanism and the messages
   described in Section 3 are the same with the following changes to the
   GS2 related elements:

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

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

   The GSS-API mechanism OIDs are:

   o  OAUTHBEARER: [[TBD: IANA -- probably in the 1.3.6.1.5.5 tree]]

   o  OAUTH10A: [[TBD: IANA -- probably in the 1.3.6.1.5.5 tree]]

   OAuth mechanims 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 property of this mechanism relies on
   successfully comparing the TLS server identity with the 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
   comparison for the mechanism.  For this reason, applications MUST
   match the TLS server identity with the target name, as discussed in
   [RFC6125].

   OAuth mechanisms do 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 mechanisms support 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 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],



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   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.















































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5.  Examples

   These examples illustrate exchanges between an IMAP and SMTP clients
   and servers.

   Note to implementers: Authorization scheme names are case
   insensitive.  One example uses "Bearer" but that could as easily be
   "bearer", "BEARER", or "BeArEr".

5.1.  Successful Bearer Token Exchange

   This example shows a successful OAuth 2.0 bearer token exchange.
   Note that line breaks are inserted for readability.


   S: * IMAP4rev1 Server Ready
   C: t0 CAPABILITY
   S: * CAPABILITY IMAP4rev1 AUTH=OAUTHBEARER
   S: t0 OK Completed
   C: t1 AUTHENTICATE OAUTHBEARER bixhPXVzZXJAZXhhbXBsZS5jb20BaG9zdD1zZX
         J2ZXIuZXhhbXBsZS5jb20BcG9ydD0xNDMBYXV0aD1CZWFyZXIgdkY5ZGZ0NHFtV
         GMyTnZiM1JsY2tCaGJIUmhkbWx6ZEdFdVkyOXRDZz09AQE=
   S: t1 OK SASL authentication succeeded

   As required by IMAP [RFC3501], the payloads are base64-encoded.  The
   decoded initial client response (with %x01 represented as ^A and long
   lines wrapped for readability) is:


   n,a=user@example.com^Ahost=server.example.com^Aport=143^A
   auth=Bearer vF9dft4qmTc2Nvb3RlckBhbHRhdmlzdGEuY29tCg==^A^A

   The same credential used in an SMTP exchange is shown below.  Note
   that line breaks are inserted for readability, and that the SMTP
   protocol terminates lines with CR and LF characters (ASCII values
   0x0D and 0x0A), these are not displayed explicitly in the example.















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   [connection begins]
   S: 220 mx.example.com ESMTP 12sm2095603fks.9
   C: EHLO sender.example.com
   S: 250-mx.example.com at your service,[172.31.135.47]
   S: 250-SIZE 35651584
   S: 250-8BITMIME
   S: 250-AUTH LOGIN PLAIN OAUTHBEARER
   S: 250-ENHANCEDSTATUSCODES
   S: 250-PIPELINING
   C: t1 AUTHENTICATE OAUTHBEARER bixhPXVzZXJAZXhhbXBsZS5jb20BaG9zdD1zZX
         J2ZXIuZXhhbXBsZS5jb20BcG9ydD0xNDMBYXV0aD1CZWFyZXIgdkY5ZGZ0NHFtV
         GMyTnZiM1JsY2tCaGJIUmhkbWx6ZEdFdVkyOXRDZz09AQE=
   S: 235 Authentication successful.
   [connection continues...]

5.2.  OAuth 1.0a Authorization with Channel Binding

   This example shows channel binding in the context of an OAuth 1.0a
   signed authorization request.  Note that line breaks are inserted for
   readability.


  S: * CAPABILITY IMAP4rev1 AUTH=OAUTH10A-PLUS SASL-IR IMAP4rev1 Server
       Ready
  S: t0 OK Completed
  C: t1 AUTHENTICATE OAUTH10A-PLUS eSxhPXVzZXJAZXhhbXBsZS5jb20BaG9zdD1zZ
        XJ2ZXIuZXhhbXBsZS5jb20BcG9ydD0xNDMBYXV0aD1PQXV0aCByZWFsbT0iRXhhb
        XBsZSIsb2F1dGhfY29uc3VtZXJfa2V5PSI5ZGpkajgyaDQ4ZGpzOWQyIixvYXV0a
        F90b2tlbj0ia2trOWQ3ZGgzazM5c2p2NyIsb2F1dGhfc2lnbmF0dXJlX21ldGhvZ
        D0iSE1BQy1TSEExIixvYXV0aF90aW1lc3RhbXA9IjEzNzEzMTIwMSIsb2F1dGhfb
        m9uY2U9IjdkOGYzZTRhIixvYXV0aF9zaWduYXR1cmU9IlNTZHRJR0VnYkdsMGRHe
        GxJSFJsWVNCd2IzUXUiAXFzPWNiZGF0YT10bHMtdW5pcXVlOlNHOTNJR0pwWnlCc
        GN5QmhJRlJNVXlCbWFXNWhiQ0J0WlhOellXZGxQd289AQE=
  S: t1 OK SASL authentication succeeded

   As required by IMAP [RFC3501], the payloads are base64-encoded.  The
   decoded initial client response (with %x01 represented as ^A and
   lines wrapped for readability) is:













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   y,a=user@example.com^A
   host=server.example.com^A
   port=143^A
   auth=OAuth realm="Example",
              oauth_consumer_key="9djdj82h48djs9d2",
              oauth_token="kkk9d7dh3k39sjv7",
              oauth_signature_method="HMAC-SHA1",
              oauth_timestamp="137131201",
              oauth_nonce="7d8f3e4a",
              oauth_signature="SSdtIGEgbGl0dGxlIHRlYSBwb3Qu"^A
   qs=cbdata=tls-unique:SG93IGJpZyBpcyBhIFRMUyBmaW5hbCBtZXNzYWdlPwo=^A^A

   In this example the signature base string with line breaks added for
   readability would be:


   POST&http%3A%2F%2Fserver.example.com:143%2F&cbdata=tls-unique:SG93I
   GJpZyBpcyBhIFRMUyBmaW5hbCBtZXNzYWdlPwo=%26oauth_consumer_key%3D9djd
   j82h48djs9d2%26oauth_nonce%3D7d8f3e4a%26oauth_signature_method%3DHM
   AC-SHA1%26oauth_timestamp%3D137131201%26oauth_token%3Dkkk9d7dh3k39s
   jv7

5.3.  Failed Exchange

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


   S: * CAPABILITY IMAP4rev1 AUTH=OAUTHBEARER SASL-IR IMAP4rev1 Server
        Ready
   S: t0 OK Completed
   C: t1 AUTHENTICATE OAUTHBEARER bixhPXVzZXJAZXhhbXBsZS5jb20BaG9zdD
         1zZXJ2ZXIuZXhhbXBsZS5jb20BcG9ydD0xNDMBYXV0aD0BAQ==
   S: + ewoic3RhdHVzIjoiNDAxIgoic2NvcGUiOiJleGFtcGxlX3Njb3BlIgp9
   C: + AQ==
   S: t1 NO SASL authentication failed

   The decoded initial client response is:


   n,a=user@example.com,^Ahost=server.example.com^A
   port=143^Aauth=^A^A

   The decoded server error response is:






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   {
   "status":"401",
   "scope":"example_scope"
   }

   The client responds with the required empty response.

5.4.  Failed Channel Binding

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


   S: * CAPABILITY IMAP4rev1 AUTH=OAUTH10A-PLUS SASL-IR IMAP4rev1 Server
        Ready
   S: t0 OK Completed
   C: t1 AUTHENTICATE OAUTH10A-PLUS eSxhPXVzZXJAZXhhbXBsZS5jb20BaG9z
        dD1zZXJ2ZXIuZXhhbXBsZS5jb20BcG9ydD0xNDMBYXV0aD0BY2JkYXRhPQEB
   S: + ewoic3RhdHVzIjoiNDEyIiwKInNjb3BlIjoiZXhhbXBsZV9zY29wZSIKfQ==
   C: + AQ==
   S: t1 NO SASL authentication failed

   The decoded initial client response is:


   y,a=user@example.com,^Ahost=server.example.com^A
   port=143^Aauth=^Acbdata=^A^A

   The decoded server response is:


   {
   "status":"412",
   "scope":"example_scope"
   }

   The client responds with the required empty response.

5.5.  SMTP Example of a failed negotiation.

   This example shows an authorization failure in an SMTP exchange.
   Note that line breaks are inserted for readability, and that the SMTP
   protocol terminates lines with CR and LF characters (ASCII values
   0x0D and 0x0A), these are not displayed explicitly in the example.






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[connection begins]
S: 220 mx.example.com ESMTP 12sm2095603fks.9
C: EHLO sender.example.com
S: 250-mx.example.com at your service,[172.31.135.47]
S: 250-SIZE 35651584
S: 250-8BITMIME
S: 250-AUTH LOGIN PLAIN OAUTHBEARER
S: 250-ENHANCEDSTATUSCODES
S: 250-PIPELINING
C: AUTH OAUTHBEARER bixhPT1zb21ldXNlckBleGFtcGxlLmNvbQFhdXRoPUJlYXJlciB2
       RjlkZnQ0cW1UYzJOdmIzUmxja0JoZEhSaGRtbHpkR0V1WTI5dENnPT0BAQ==
S: 334 eyJzdGF0dXMiOiI0MDEiLCJzY2hlbWVzIjoiYmVhcmVyIG1hYyIsInNjb3BlIjoia
       HR0cHM6Ly9tYWlsLmdvb2dsZS5jb20vIn0K
C: AQ==
S: 535-5.7.1 Username and Password not accepted. Learn more at
S: 535 5.7.1 http://support.example.com/mail/oauth
[connection continues...]

   The server returned an error message in the 334 SASL message, the
   client responds with the required empty response, and the server
   finalizes the negotiation.






























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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.

   The channel binding in this mechanism has different properties based
   on the authentication scheme used.  The integrity guarantee for
   channel binding depends on the quality of the guarantee in the the
   authorization scheme.

   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.

   Tokens have a lifetime associated with them.  Reducing the lifetime
   of a token provides security benefits in the 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.















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7.  IANA Considerations

7.1.  SASL Registration

   The IANA is requested to register the following SASL profile:

      SASL mechanism profile: OAUTHBEARER

      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: OAUTH10A

      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: OAUTH10A-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






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7.2.  GSS-API Registration

   IANA is further requested to assign an OID for thESE GSS mechanismS
   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.













































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8.  References

8.1.  Normative References

   [I-D.ietf-oauth-v2]
              Hardt, D., "The OAuth 2.0 Authorization Framework",
              draft-ietf-oauth-v2-31 (work in progress), August 2012.

   [I-D.ietf-oauth-v2-bearer]
              Jones, M. and D. Hardt, "The OAuth 2.0 Authorization
              Framework: Bearer Token Usage",
              draft-ietf-oauth-v2-bearer-23 (work in progress),
              August 2012.

   [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.

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

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

   [RFC5234]  Crocker, D. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", STD 68, RFC 5234, January 2008.

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

   [RFC5321]  Klensin, J., "Simple Mail Transfer Protocol", RFC 5321,



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              October 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.

8.2.  Informative References

   [I-D.ietf-oauth-v2-http-mac]
              Hammer-Lahav, E., "HTTP Authentication: MAC Access
              Authentication", draft-ietf-oauth-v2-http-mac-01 (work in
              progress), February 2012.

   [I-D.jones-appsawg-webfinger]
              Jones, P., Salgueiro, G., and J. Smarr, "WebFinger",
              draft-jones-appsawg-webfinger-06 (work in progress),
              June 2012.

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
















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Appendix A.  Acknowlegements

   The authors would like to thank the members of the Kitten working
   group, and in addition and specifically: Simon Josefson, Torsten
   Lodderstadt, Ryan Troll, and Nico Williams.














































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Appendix B.  Document History

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

   -06

   o  Removed the user field.  Fixed the examples again.

   o  Added canonicalization language.

   o

   -05

   o  Fixed the GS2 header language again.

   o  Separated out different OAuth schemes into different SASL
      mechanisms.  Took out the scheme in the error return.  Tuned up
      the IANA registrations.

   o  Added the user field back into the SASL message.

   o  Fixed the examples (again).

   o

   -04

   o  Changed user field to be carried in the gs2-header, and made gs2
      header explicit in all cases.

   o  Converted MAC examples to OAuth 1.0a.  Moved MAC to an informative
      reference.

   o  Changed to sending an empty client response (single control-A) as
      the second message of a failed sequence.

   o  Fixed channel binding prose to refer to the normative specs and
      removed the hashing of large channel binding data, which brought
      mroe problems than it solved.

   o  Added a SMTP examples for Bearer use case.

   -03

   o  Added user field into examples and fixed egregious errors there as
      well.




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   o  Added text reminding developers that Authorization scheme names
      are case insensitive.

   -02

   o  Added the user data element back in.

   o  Minor editorial changes.

   -01

   o  Ripping out discovery.  Changed to refer to I-D.jones-appsawg-
      webfinger instead of WF and SWD older drafts.

   o  Replacing HTTP as the message format and adjusted all examples.

   -00

   o  Renamed draft into proper IETF naming format now that it's
      adopted.

   o  Minor fixes.





























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Authors' Addresses

   William Mills
   Yahoo! Inc.


   Phone:
   Email: wmills@yahoo-inc.com


   Tim Showalter


   Phone:
   Email: tjs@psaux.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

























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