OAuth Working Group                                  T. Lodderstedt, Ed.
Internet-Draft                                       Deutsche Telekom AG
Intended status: Standards Track                               S. Dronia
Expires: May 28, July 11, 2013
                                                           M. Scurtescu
                                                       November 24, 2012
                                                         January 7, 2013

                            Token Revocation


   This document proposes an additional endpoint for OAuth authorization
   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. authorization.

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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   This Internet-Draft will expire on May 28, July 11, 2013.

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   Copyright (c) 2012 2013 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  Token Revocation  . . . . . . . . . . . . . . . . . . . . . . . 3
     2.1.  Cross-Origin Support  . . . . . . . . . . . . . . . . . . . 5
   3.  Implementation Note . . . . . . . . . . . . . . . . . . . . . . 5
   4.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 6
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
   6.  Security Considerations . . . . . . . . . . . . . . . . . . . . 6
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 7
     7.1.  Normative References  . . . . . . . . . . . . . . . . . . . 7
     7.2.  Informative References  . . . . . . . . . . . . . . . . . . 7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 7 8

1.  Introduction

   The OAuth 2.0 core specification [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 a string representing an access
   grant authorization
   issued by a the resource owner to a particular the client.  A revocation request
   will invalidate the actual token and, if applicable, other tokens
   based on the same access grant authorization and the
   access grant authorization itself.

   From an end-user's perception, perspective, OAuth is often used to log into a
   certain site or app.  This revocation mechanism allows a client to
   invalidate its tokens if the end-user logs out, changes identity, or
   uninstalls the respective app.  Notifying the authorization server
   that the token is no longer needed allows the authorization server to
   clean up data associated with that token (e.g. session data) and the
   underlying access grant. authorization.  This behavior prevents a situation where
   there is still a valid access grant authorization for a particular client which
   the end user is not aware of.  This way, token revocation prevents
   abuse of abandoned tokens and facilitates a better end-user
   experience since invalidated access grants authorization will no longer turn up in
   a list of
   access grants authorizations 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

   Implementations MUST support the revocation of refresh tokens and
   SHOULD support the revocation of access tokens (see Implementation

   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 [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 then verifies whether the client is
   authorized to revoke the particular token.  These checks are used to
   validate whether the token being presented has been
   was issued to the client presenting it. making the revocation request.  If this
   validation fails, the request is refused and the client is informed
   of the error by the authorization server as described below.

   In the next step, the authorization server invalidates the token.
   The client MUST NOT use this token again after revocation.

   Depending on the authorization server's revocation policy, the
   revocation of a particular token may cause the revocation of related
   tokens and the respective access grant. underlying authorization.  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 authorization (see
   Implementation Note).

   The client MUST NOT use the token 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  The error presentation conforms
   to revoke the particular token.  For all
   other error conditions, a status code 400 is used along with an error
   response as defined defintion in section 5.2. 5.2 of [RFC6749].

   The following additional 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 revocation end-point SHOULD support CORS [W3C.WD-cors-20120403]
   if it is aimed at use in combination with user-agent-based

   In addition, for interoperability with legacy user-
   agents, user-agents, it MAY
   offer JSONP [jsonp] by allowing GET requests with an additional

   callback  OPTIONAL.  The qualified name of a JavaScript function.

   Example request:


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


   Successful response:


   Error response:


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

3.  Implementation Note

   Depending on

   OAuth 2.0 allows deployment flexibility with respect to the authorization server's token design, revocation style of
   access tokens.  The access tokens might may be a costly process.  For example, revocation of self-contained so that an
   resource server needs no further interaction with an authorization
   server issuing these tokens to perform an authorization decision of
   the client requesting access to a protected resource.  A system
   design may, however, instead use access tokens that are handles
   referring to authorization data stored at the authorization server.
   This consequently requires (time-consuming) backend calls
   between a resource and authorization server on every to issue a request to
   resource respective authorization server or to push notifications from retrieve the content of the
   access token every time a client presents an access token.

   While these are not the only options they illustrate the implications
   for revocation.  In the latter case the authorization server is able
   to revoke an access token previously issued to a client when the affected
   resource servers.  Alternatively, server relays a received access token.  In the former case
   some (currently non-standardized) backend interaction between the
   authorization servers server and the resource server may choose be used when
   immediate access token revocation is desired.  Another design
   alternative is to issue short living short-lived access tokens, which can be
   refreshed at any time using the corresponding refresh tokens.  In this case,  This
   allows the authorization server to impose a client would revoke limit on the refresh token and time revoked
   access tokens issued based on this particular refresh token are at
   most valid until expiration.  Whether this is an viable option or
   whether access in use.

   Which approach of token revocation is required should be decided based chosen will depend on the
   overall system design and on the application service provider's risk
   analysis.  The cost of revocation in terms of required state and
   communication overhead is ultimately the result of the desired
   security properties.

4.  Acknowledgements

   We would like to thank Peter, Mauritius, Amanda Anganes, Mark Wubben,
   Hannes Tschofenig, Michiel de Jong, Doug Foiles, Paul Madsen, George
   Fletcher, Sebastian Ebling, Christian Stuebner, Brian Campbell, Igor
   Faynberg, Lukas Rosenstock, and Justin Richer for their valuable

5.  IANA Considerations

   This draft includes no request to IANA.

6.  Security Considerations

   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
   into account when conducting their security risk analysis.

   Cleaning up tokens using revocation contributes to overall security
   and privacy since it reduces the likelihood 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 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 should be in place for the token endpoint as
   well, MUST be applied to the revocation endpoint. endpoint (see
   [I-D.ietf-oauth-v2-threatmodel], section

   A malicious client may attempt to guess valid tokens on this
   endpoints.  As endpoint
   by making revocation requests against potential token strings.
   According to this specification, a pre-requisite, the client either requires client's request must contain a
   client_id client_id, in the case of a public client client, or valid client
   credentials, in the credentials case of a confidential client.  An sucessful attempt would result in  The token being
   revoked must also belong to the revocation requesting client.  If an attacker is
   able to successfully guess a public client's client_id and one of
   their tokens, or a private client's credentials and one of their
   tokens, they could do much worse damage by using the token elsewhere
   than by revoking it.  If they chose to revoke the
   respective token, thus causing the
   legitimate client to will lose its
   authorization.  The malicious client does not gain authorization and will need to prompt
   the user again.  No further
   advantages. damage is done and the guessed token is
   now worthless.

7.  References

7.1.  Normative References

   [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.

7.2.  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