OAuth Working Group                                  T. Lodderstedt, Ed.
Internet-Draft                                       Deutsche Telekom AG
Intended status: Standards Track                               S. Dronia
Expires: April 9, May 22, 2013
                                                           M. Scurtescu
                                                         October 6,
                                                       November 18, 2012

                            Token Revocation


   This draft document proposes an additional endpoint for OAuth authorization
   servers for revoking tokens.
   servers, which allows clients to notify the authorization server that
   a previously obtained refresh or access token is no longer needed.
   This allows the authorization server to cleanup security credentials.
   A revocation request will invalidate the actual token and, if
   applicable, other tokens based on the same access grant.

Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC 2119 [RFC2119].

Status of this Memo

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

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  Token Revocation  . . . . . . . . . . . . . . . . . . . . . . . 3
     2.1.  Cross-Origin Support  . . . . . . . . . . . . . . . . . . . 5
   3.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 5
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
   5.  Security Considerations . . . . . . . . . . . . . . . . . . . . 6
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 6
     6.1.  Normative References  . . . . . . . . . . . . . . . . . . . 6
     6.2.  Informative References  . . . . . . . . . . . . . . . . . . 6 7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 6 7

1.  Introduction

   The OAuth 2.0 core specification [I-D.ietf-oauth-v2] [RFC6749] defines several ways for a
   client to obtain refresh and access tokens.  This specification
   supplements the core specification with a mechanism to revoke both
   types of tokens.  A token is the external representation of an access
   grant issued by a resource owner to a particular client.  A
   revocation request may discard will invalidate the actual token as well as and, if
   applicable, other tokens based on the same access grant and the
   access grant itself.

   From an end-user's perception, OAuth is often used to log into a
   certain site or app.  This mechanism facilitates the following use cases:

   o  The end-user triggers revocation from within the mechanism allows a client that sends
      the appropriate revocation request to
   invalidate its tokens if the autorization server.
      The request causes end-user logs out, changes identity, or
   uninstalls the removal of respective app.  Notifying the client's access grant authorization server
   that the
      particular token refers to.  From is no longer needed allows the end-user's perspective, this
      looks like a "logout" or "reset" function.  This use case makes it
      even more comfortable authorization server to
   cleanup data associated with that token (e.g. session data) and the end-user to revoke his
   underlying access grant
      immediately via the client.

   o  In contrast to revocation by a client, the authorization server
      (or grant.  This prevents a related entity) may offer its end-users situation, where there is
   still a self-care portal
      to delete valid access grants given to clients independent of any token
      storing devices.  Such a portal offers grant for that particular client, which the possibility to an end-
   user to look at and revoke all access grants he once authorized.
      In cases the token storing device is not available, e.g. it is
      lost or stolen, revocation by a self-care portal is the only
      possibility to limit or avoid abuse.

   In the end, security, usability, and ease of use are increased by
   token revocation.

   By using an additional endpoint, the aware of.  This way, token revocation endpoint,
   clients can request the revocation prevents abuse of
   abandoned tokens and facilitates a particular token.  Compliant
   implementation MUST support the revocation better end-user experience since
   invalidated access grants will no longer turn up in a list of refresh tokens, access
   token revocation MAY be supported.
   grants the authorization server might present to the end-user.

2.  Token Revocation

   The client requests the revocation of a particular token by making an
   HTTP POST request to the token revocation endpoint.  The location of
   the token revocation endpoint can be found in the authorization
   server's documentation.  The token endpoint URI MAY include a query

   Since requests to

   Compliant implementation MUST support the token revocation endpoint result in the
   transmission of plain text credentials in the HTTP request, refresh
   tokens, access token revocation SHOULD be supported.

   Note: Depending on the authorization server MUST server's token design,
   revocation of access tokens might be a costly process.  For example,
   revocation of self-contained access tokens requires (time-consuming)
   backend calls between resource and authorization server on every
   request to the resource server or to push notifications from the
   authorization server to the affected resource servers.
   Alternatively, authorization servers may choose to issue short living
   access tokens, which can be refreshed at any time using the
   corresponding refresh tokens.  In this case, a client would revoke
   the refresh token and access tokens issued based on this particular
   refresh token are at most valid until expiration.  Whether this is an
   viable option or whether access token revocation is required should
   be decided based on the service provider's risk analysis.

   Since requests to the token revocation endpoint result in the
   transmission of plain text credentials in the HTTP request, the
   authorization server MUST require the use of a transport-layer
   security mechanism when sending requests to the token revocation
   endpoints.  The authorization server MUST support TLS 1.0
   ([RFC2246]), SHOULD support TLS 1.2 ([RFC5246]) and its future
   replacements, and MAY support additional transport-layer mechanisms
   meeting its security requirements.

   The client constructs the request by including the following
   parameters using the "application/x-www-form-urlencoded" format in
   the HTTP request entity-body:

   token   REQUIRED.  The token that the client wants to get revoked.
           Note: the authorization server is supposed to detect the
           token type automatically.

   The client also includes its authentication credentials as described
   in Section 2.3. of [I-D.ietf-oauth-v2]. [RFC6749].

   For example, a client may request the revocation of a refresh token
   with the following request (line breaks are for display purposes

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


   The authorization server first validates the client credentials (in
   case of a confidential client) and verifies whether the client is
   authorized to revoke the particular token.  It therefore validates
   whether this token based on the client
   identity and its policy.  For example, only the client the token has had been issued for might be allowed to revoke it.  It is also
   conceivable to allow a dedicated user self-care portal to revoke all
   kinds of tokens. this client.

   In the next step, the authorization server invalidates the token and
   the respective access grant.  If the particular token is a refresh
   token and the authorization server supports the revocation of access
   tokens, then the authorization server SHOULD also invalidate all
   access tokens based on the same access grant.

   Whether the

   Note: for considerations regarding access token revocation takes effect instantly or with some delay
   depends on the architecture of the particular deployment. see note

   The client MUST NOT make any assumptions about the timing and MUST NOT use the token again. again after revocation.

   The authorization server indicates a successful processing of the
   request by a HTTP status code 200.  Status code 401 indicates a
   failed client authentication, whereas a status code 403 is used if
   the client is not authorized to revoke the particular token.  For all
   other error conditions, a status code 400 is used along with an error
   response as defined in section 5.2. of [I-D.ietf-oauth-v2]. [RFC6749].  The following
   error codes are defined for the token revocation endpoint:

   unsupported_token_type  The authorization server does not support the
           revocation of the presented token type.  I.e. the client
           tried to revoke an access token on a server not supporting
           this feature.

   invalid_token  The presented token is invalid.

2.1.  Cross-Origin Support

   The revokation end-point SHOULD support CORS [W3C.WD-cors-20120403]
   if it is aimed at use in combination with user-agent-based
   applications.  In addition, for interoperability with legacy user-
   agents, it MAY offer JSONP [jsonp] by allowing GET requests with an
   additional parameter:

   callback  The qualified name of a JavaScript function.

   Example request:


   Successful response:


   Error response:


   Clients should be aware that when relying on JSONP, a malicious
   revokation end-point may attempt to inject malicious code into the

3.  Acknowledgements

   We would like to thank Hannes Tschofenig, Michiel de Jong, Doug
   Foiles, Paul Madsen, George Fletcher, Sebastian Ebling, Christian
   Stuebner, Brian Campbell, Igor Faynberg, Lukas Rosenstock, and Justin
   P. Richer for their valuable feedback.

4.  IANA Considerations

   This draft includes no request to IANA.

5.  Security Considerations

   All relevant

   If the authorization server does not support access token revocation,
   access tokens will not be immediately invalidated when the
   corresponding refresh token is revoked.  Deployments MUST take this
   in account when conducting their security risk analysis.

   Cleaning up tokens using revocation contributes to overall security
   and privacy since it reduces the liklyhood for abuse of abandoned
   tokens.  This specification in general does not intend to provide
   countermeasures against token theft and abuse.  For a discussion of
   respective threats and countermeasures, consult the security
   considerations have been given in section 10 of the OAuth core specification
   [RFC6749] and the OAuth threat model document

   Malicious clients could attempt to use the new endpoint to launch
   denial of service attacks on the authorization server.  Appropriate
   countermeasures, which must be in place for the token endpoint as
   well, should be applied to the revocation endpoint.

   A malicious client may attempt to guess valid tokens on this
   endpoints.  As a pre-requisite, the client either requires a valid
   client_id of a public client or the credentials of a confidential
   client.  An sucessful attempt would result in the revocation of the
   respective token, thus causing the
   functional specification. legitimate client to loss its
   authorization.  The malicious client does not gain further

6.  References

6.1.  Normative References

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

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

   [RFC2246]  Dierks, T. and C. Allen, "The TLS Protocol Version 1.0",
              RFC 2246, January 1999.

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

   [RFC6749]  Hardt, D., "The OAuth 2.0 Authorization Framework",
              RFC 6749, October 2012.

6.2.  Informative References

              Lodderstedt, T., McGloin, M., and P. Hunt, "OAuth 2.0
              Threat Model and Security Considerations",
              draft-ietf-oauth-v2-threatmodel-08 (work in progress),
              October 2012.

              Kesteren, A., "Cross-Origin Resource Sharing", World Wide
              Web Consortium LastCall WD-cors-20120403, April 2012,

   [jsonp]    Ippolito, B., "Remote JSON - JSONP", December 2005.

Authors' Addresses

   Torsten Lodderstedt (editor)
   Deutsche Telekom AG

   Email: torsten@lodderstedt.net

   Stefanie Dronia

   Email: sdronia@gmx.de

   Marius Scurtescu

   Email: mscurtescu@google.com