KITTEN                                                          W. Mills
Internet-Draft                                              T. Showalter                                               Yahoo! Inc.
Intended status: Standards Track                             Yahoo! Inc.                            T. Showalter
Expires: May 17, December 1, 2012
                                                           H. Tschofenig
                                                  Nokia Siemens Networks
                                                       November 14, 2011
                                                            May 30, 2012

                 A SASL and GSS-API Mechanism for OAuth
                  draft-ietf-kitten-sasl-oauth-00.txt
                    draft-ietf-kitten-sasl-oauth-01

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 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, and additionally defines
   authorization and token issuing endpoint discovery. 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."
   This Internet-Draft will expire on May 17, December 1, 2012.

Copyright Notice

   Copyright (c) 2011 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
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   described in the Simplified BSD License.

Table of Contents

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

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 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 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 -------|               |
        |        |                               +---------------+
        |        |
        |        |                               +---------------+
        |        |--(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], 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
   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 for OAuth, but it conforms to
   the new bridge between SASL and 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
   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,
      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 client will genrally need to determine the optional discovery exchange steps that may happen
   authentication endpoints (and perhaps the service endpoints) before
   the OAuth 2.0 protocol exchange messages in steps (A)-(D) are
   executed.  Steps (E)  The discovery of the resource owner and (F) also defined in authorization
   server endpoints is outside the scope of this specification.

                                                              ----+
   +--------+                                  +---------------+  |
   |        |--(A)-- Authorization Request --->|   Resource    |  |  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) +---------------+  |
   |        |                                                 ----+
   |        |
   |        |                                                 ----+
   |        |        (Optional discovery)                                  +---------------+  |
   |        |--(1)------- User Name  --------->|               |  |
   | Client |                                  |               |  |
   |        |<-(2)------ Authentication -------|               |  |
   |        |          endpoint information                                  |    Resource               |  |OAuth
   |        |                                  |     Server    |  |over
   |        |--(E)------ Access Token -------->|    Resource   |  |SASL/  |over
   |        |                                  |     Server    |  |GSS-  |SASL/
   |        |<-(F)---- Protected Resource -----|               |  |GSS-
   |        |                                  |               |  |API
   +--------+                                  +---------------+  |
                                                              ----+

                     Figure 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], or [I-D.jones-simple-web-discovery]) and
      configuration information exchanged in-band between the 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 [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.  OAuth SASL Mechanism Specification

   SASL is used as a generalized authentication method in a variety of
   application layer protocols.  This document defines two SASL
   mechanisms for usage with OAuth: "OAUTH" and "OAUTH-PLUS".  The
   "OAUTH" SASL mechanism provides bearer token alike semantic enables OAuth authorizattion schemes for SASL
   while SASL,
   "OAUTH-PLUS" provides a semantic similar to OAuth MAC
   authentication by utilizing a adds channel binding mechanism [RFC5056].

3.1.  Channel Binding

   If the specification [RFC5056] capability for the underlying authorization scheme requires
   a additional
   security layer, such as TLS [RFC5246], the server SHOULD only offer guarantees.

3.1.  Initial Client Response

   Client responses are a mechanism where channel binding can key/value pair sequence.  These key/value
   pairs carry the equivalent values form an HTTP context in order to be enabled.
   able to complete an OAuth style HTTP authorization.  The channel binding data is computed by the client based on it's
   choice of preferred channel binding type.  As specified ABNF
   [RFC2234] syntax is:

     kvsep          = %x01
     key            = 1*ALPHA
     value          = *(VCHAR | SP | HTAB | CR | LF )
     kvpair         = key "=" value kvsep
     client_resp    = 1*kvpair kvsep

   The following key/value pairs are defined 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. client response:

      auth (REQUIRED):  The channel binding payload is of the
   raw data from the channel binding type if the raw channel binding
   data is less than 500 bytes.  If the raw channel binding data is 500
   bytes or larger then a SHA-1 [RFC3174] hash of the raw channel
   binding data is computed.

   If the client is using tls-unique HTTP Authorization header for a channel binding then the raw
   channel binding data 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, which will frequently be 500 bytes or 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 equivalent 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): OAuth authroization.

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

      Authorization (REQUIRED):  An HTTP Authorization 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):

      port:  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 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.

3.4.  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 the port number represented as a decimal positive
         integer string without leading zeros to token which equates to the SASL authentication
   identity, and is authenticated using the shared secret.  The client
         connected.

   In authorization identity in the OAuth 1.0a case is carried in schemes that use signatures, the token
   (per client MUST send
   host and port number key/values, and the requirement above), which SHOULD validated independently.
   The server MAY use a consumer key or other comparable identity MUST fail
   authorization request requiring signatures that do not have host and
   port values.

3.1.1.  Reserved Key/Values in OAUTH

   In the OAUTH mechanism values for path, query string and post body
   are assigned default values.  OAuth authorization scheme as schemes MAY define
   usage of these in the SASL authentication identity.  If
   an appropriate authentication identity is not available the server
   MUST context and extend this specification.
   For OAuth schemes that use the identity asserted in the token.

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 signatures the discovery information default values MUST
   be for that user.
   Discovery information is used unless explict values are provided by the server to in the client to
   allow a client to discover the appropriate OAuth authentication and
   token endpoints. response.
   The client then uses that information to obtain the
   access token needed following key values are reserved for OAuth authentication.  The client SHOULD
   cache and re-use future use:

      path (RESERVED):  HTTP path data, the user specific discovery information for service
   endpoints.

   Discovery information makes use of both default value is "/".

      qs (RESERVED):  HTTP query string, the WWW-Authenticate header
   as defined in default value is "".

      post (RESERVED):  HTTP Authentication: Basic and Digest Access
   Authentication [RFC2617] and Link headers as defined in [RFC5988]. post data, the default value is "".

3.2.  Server's Response

   The following elements are defined for discovery information:

   WWW-Authenticate  A WWW-Authenticate header server validates the response per the specification for each authentication the
   authorization scheme supported by used.  If the server.  Authentication authorization scheme names are
      case insensitive.  The following [RFC2617] authentication used includes
   signing of the request 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 must provide a client
   response that satisfies the data requirements for the resource.

   oauth2-authenticator  An [RFC5988] Link header specifying scheme in use.

   In the
      [I-D.ietf-oauth-v2] authentication endpoint.  This link has an
      OPTIONAL link-extension "scheme", if included this link applies
      ONLY to OAUTH-PLUS mechanism the specified scheme.

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

   oauth-initiate  (Optional) An [RFC5988] Link header specifying channel binding unique prefix, and extracts the
      OAuth1.0a [RFC5849] initiation endpoint.  The server MUST send
      this if "OAuth" is included in
   raw channel biding data based on the supported list channel binding type used.  It
   then computes it's own copy of HTTP
      authentication schemes for the server.

   oauth-authorize  (Optional) An [RFC5988] Link header specifying channel binding payload and
   compares that to the
      OAuth1.0a [RFC5849] authentication endpoint. payload sent by the client in the cbdata key/
   value.  Those two must be equal for channel binding to succeed.

   The server MUST send
      this if "OAuth" is included in responds to a successfully verified client message by
   completing the supported list of HTTP SASL negotiation.  The authentication schemes for scheme MUST
   carry the server.

   oauth-token  (Optional) An [RFC5988] Link header specifying user ID to be used as the
      OAuth1.0a [RFC5849] token endpoint. authorization identity (identity
   to act as).  The server MUST send this if
      "OAuth" is included in use the supported list of HTTP authentication
      schemes for ID obtained from the server.  This link type has one link-extension
      "grant-types" which is a space separated list 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 the this is OAuth 2.0
      grant types that can be used at 1.0a
   [RFC5849] where the consumer key (oauth_consumer_key) identifies the
   entity using to token endpoint which equates to obtain a
      token.

   Usage of the URLs provided SASL authentication
   identity, and is authenticated using the shared secret.  The
   authorization identity in the discovery information OAuth 1.0a case is defined carried in the relevant specifications.  If token
   (per the requirement above), which SHOULD validated independently.
   The server supports multiple
   authenticators the discovery information returned for unknown users
   MUST be consistent with MAY use a consumer key, a value derived from it, or other
   comparable identity in the discovery information for known users to
   prevent user enumeration.  The OAuth 2.0 specification
   [I-D.ietf-oauth-v2] supports multiple types of authorization scheme as the SASL
   authentication schemes
   and identity.  If an appropriate authentication identity
   is not available the server MUST specify at least one supported use the authorization identity as
   the wuthentication identity.

3.2.2.  Server response to failed authentication.

   For a failed authentication
   scheme in the discovery information.  The server MAY support multiple
   schemes returns a JSON [RFC4627]
   formatted error result, and MAY support schemes not listed fails the authentication.  The error
   result consists of the following values:

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

      scope (OPTIONAL):  The OAuth scope required to access the service.

   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 are be defined by
   the resource owner and provided in service documentation or discovery
   information (which is beyond the scope of this memo).

3.6.  If not present
   then the client SHOULD presume an empty scope (unscoped token) is
   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.

3.3.  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 or define default values for the data elements from an HTTP style format specifically to support
   request which allow the signature type
   authentication, but this is extremely limited. base string to be constructed
   properly.  The default HTTP style
   request is limited to a path of "/".  This mechanism is in "/" and the SASL
   model, but default post body is designed
   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 specific directory.

   Using the example in the MAC specification
   [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 %x01 shown as ^A and long lines wrapped for readability) below:

   host=server.example.com^A
   port=143^A
   auth=MAC token="h480djs93hd8",timestamp="137131200",nonce="dj83hs9s",
            signature="YTVjyNSujYs1WsDurFnvFi4JK6o="^A^A

   The normalized request string would be constructed per the MAC
   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

3.4.  Channel Binding

   If the specification for the underlying authorization scheme requires
   a security layer, such as TLS [RFC5246], the server SHOULD only offer
   a mechanism where channel binding can be enabled.

   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 if the raw channel binding
   data is less than 500 bytes.  If the raw channel binding data is 500
   bytes or larger then a SHA-1 [RFC3174] hash of the raw channel
   binding data is computed.

   If the client is using tls-unique for a channel binding then the example in raw
   channel binding data equals the MAC specification
   [I-D.ietf-oauth-v2-http-mac] as a starting point, on an IMAP server
   running on port 143 and given first TLS finished message.  This is
   under 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 500 byte limit, so the channel binding payload sent to the
   server would be constructed per the MAC
   specification [I-D.ietf-oauth-v2-http-mac]. base64 encoded first TLS finished message.

   In this example the
   normalized request string with case where the new line separator character client has chosen tls-endpoint, the raw channel
   binding data 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 the certificate of the server the client connected
   to, which will frequently be 500 bytes or more.  If it is then the
   channel binding payload is the base64 encoded SHA-1 hash of the
   server certificate.

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.

   The SASL OAuth mechanism is also a GSS-API mechanism and 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

   2.  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 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 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].

   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 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= aG9zdD1zZXJ2ZXIuZXhhbXBsZS5jb20BcG9ydD0xNDMB
         YXV0aD1CRUFSRVIgdkY5ZGZ0NHFtVGMyTnZiM1JsY2tCaGJIUmhkbWx6ZEdFdVk
         yOXRDZz09AQE=
   S: +
   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:

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

   host=server.example.com^Aport=143^A
   auth=BEARER "vF9dft4qmTc2Nvb3RlckBhbHRhdmlzdGEuY29tCg=="^A^A

   The line containing just a "+" and a space is an empty response from
   the server.  This response contains discovery error information, and in the
   success case no discovery information is necessary so the error 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 aG9zdD1zZXJ2ZXIuZXhhbXBsZS5jb20BcG9ydD0xNDMBYXV0a
   D1NQUMgdG9rZW49Img0ODBkanM5M2hkOCIsdGltZXN0YW1wPSIxMzcxMzEyMDAiLG5vbm
   NlPSJkajgzaHM5cyIsc2lnbmF0dXJlPSJZVFZqeU5TdWpZczFXc0R1ckZudkZpNEpLNm8
   9IgFjYmRhdGE9U0c5M0lHSnBaeUJwY3lCaElGUk1VeUJtYVc1aGJDQnRaWE56WVdkbFB3
   bz0BAQ==
S: +
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:

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

   -
   host=server.example.com^A
   port=143^A
   auth=MAC token="h480djs93hd8",timestamp="137131200",nonce="dj83hs9s",
            signature="YTVjyNSujYs1WsDurFnvFi4JK6o="^A
   cbdata=SG93IGJpZyBpcyBhIFRMUyBmaW5hbCBtZXNzYWdlPwo=^A^A

   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.

5.3.  Failed Exchange

   This example shows a failed exchange because of the empty
   Authorization header, which is how a client can query for discovery
   information. the needed
   scope.  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== aG9zdD1zZXJ2ZXIuZXhhbXBsZS5jb20BcG9ydD0xND
      MBYXV0aD0BAQ==
   S: + SFRUUC8xLjEgNDAxIFVuYXV0aG9yaXplZA0KV1dXLUF1dGhlbnRpY2F0ZTogQk
      VBUkVSIHJlYWxtPSJleGFtcGxlLmNvbSINCkxpbms6IDxodHRwczovL2xvZ2luLn
      lhaG9vLmNvbS9vYXV0aD4gcmVsPSJvYXV0aDItYXV0aGVudGljYXRvciIgIA0KTG
      luazogPGh0dHBzOi8vbG9naW4ueWFob28uY29tL29hdXRoPiByZWw9Im91YXRoMi
      10b2tlbiINCg0K ewoic3RhdHVzIjoiNDAxIiwKInNjb3BlIjoiZXhhbXBsZV9zY29wZSIKfQo=
   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:

   host=server.example.com^Aport=143^Aauth=^A^A

   The decoded server discovery error 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"

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

5.4.  Failed Channel Binding

   This example shows a channel binding failure in a discovery an empty 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 aG9zdD1zZXJ2ZXIuZXhhbXBsZS5jb20BcG9ydD0xND
      MBYXV0aD0BY2JkYXRhPQEB
   S: + SFRUUC8xLjEgNDEyIFByZWNvbmRpdGlvbiBGYWlsZWQNCg0KDQo= ewoic3RhdHVzIjoiNDEyIiwKInNjb3BlIjoiZXhhbXBsZV9zY29wZSIKfQ==
   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:

   host=server.example.com^Aport=143^Aauth=^Acbdata=^A^A

   The decoded server response is:

   HTTP/1.1 412 Precondition Failed

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

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.  Channel binding to TLS with a bearer
   token provides only a binding to the TLS layer.  Authentication
   schemes like MAC tokens have can implement a signature over the channel
   binding information.  These provide additional protection against a
   man in the 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 taken in different domains.  For instance,
   a site might operate their authentication service in-house, but
   outsource their mail systems
   the authenticated channel are appropriate to an external entity. the strength of the
   presented credential.

   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.

7.3.1.  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]

7.3.2.  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", 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.

7.3.3.  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: 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 OAuth 1.0a endpoint used IANA is requested to initiate register the sequence, following SASL profile:

      SASL mechanism profile: OAUTH-PLUS

      Security Considerations: See this
      temporary request is what document

      Published Specification: See this document

      For further information: Contact the user approves to grant access to authors of this document.

      Owner/Change controller: the
      resource.

   o  Application Data:

7.3.4.  OAuth 1.0a Authorization Endpoint

   o  Relation Name: oauth-authorize

   o  Description: The OAuth 1.0a authorization endpoint used IETF

      Note: None

7.2.  GSS-API Registration

   IANA is further requested to approve assign an access request.

   o  Reference:

   o  Notes:

   o  Application Data:

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 OID for
      access.

   o  Reference:

   o  Notes:

   o  Application Data: 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.

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

   -01

   o  Filling  Ripping out Channel Binding

   o  Added text clarifying how discovery.  Changed to bind refer to the 2 kinds I-D.jones-appsawg-
      webfinger instead of SASL
      identities.

   -01 WF and SWD older drafts.

   o  Bringing this into line with draft 12 of the core spec,  Replacing HTTP as the bearer
      token spec, message format and references the MAC token spec adjusted all examples.

   -00

   o  Changing discovery over to using the Link header construct from
      RFC5988.  Renamed draft into proper IETF naming format now that it's
      adopted.

   o  Added the seeds of channel binding.  Minor fixes.

   -00

   o  Initial revision

9.  References

9.1.  Normative References

   [I-D.ietf-oauth-v2]
              Hammer-Lahav, E., Recordon, D., and D. Hardt, "The OAuth
              2.0 Authorization Protocol", draft-ietf-oauth-v2-22 Framework", draft-ietf-oauth-v2-26 (work
              in progress), September 2011. May 2012.

   [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-14
              draft-ietf-oauth-v2-bearer-19 (work in progress),
              November 2011.
              April 2012.

   [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 draft-ietf-oauth-v2-http-mac-01 (work in
              progress),
              May 2011. February 2012.

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

   [RFC2234]  Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", RFC 2234, November 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.

   [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-17 (work in progress),
              September 2011.

   [I-D.jones-simple-web-discovery]

   [I-D.jones-appsawg-webfinger]
              Jones, M. P., Salgueiro, G., and Y. Goland, "Simple Web Discovery (SWD)",
              draft-jones-simple-web-discovery-01 J. Smarr, "WebFinger",
              draft-jones-appsawg-webfinger-05 (work in progress),
              July 2011.
              May 2012.

   [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 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