Abstract
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.
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 . . . . . . . . . . . . . . . . . . . . . . . . 7
Lodderstedt, et al. Expires May 28, 2013 [Page 2]
Internet-Draft Token Revocation November 2012
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 an access
grant issued by a resource owner to a particular client. A
revocation request will invalidate the actual token 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 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. This behavior prevents a situation where
there is still a valid access grant 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 will no longer turn up in a list of
access 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
component.
Implementations MUST support the revocation of refresh tokens and
SHOULD support the revocation of access tokens (see Implementation
Note).
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
Lodderstedt, et al. Expires May 28, 2013 [Page 3]
Internet-Draft Token Revocation November 2012
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
only):
POST /revoke HTTP/1.1
Host: server.example.com
Content-Type: application/x-www-form-urlencoded
Authorization: Basic czZCaGRSa3F0MzpnWDFmQmF0M2JW
token=45ghiukldjahdnhzdauz&
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. These checks are used to
validate whether the token being presented has been issued to the
client presenting it.
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 (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 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 [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.
Lodderstedt, et al. Expires May 28, 2013 [Page 4]
Internet-Draft Token Revocation November 2012
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:
https://example.com/revoke?token=45ghiukldjahdnhzdauz&
callback=package.myCallback
Successful response:
package.myCallback();
Error response:
package.myCallback({"error":"invalid_token"});
Clients should be aware that when relying on JSONP, a malicious
revokation end-point may attempt to inject malicious code into the
client.
3. Implementation Note
Depending on the authorization 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.
Lodderstedt, et al. Expires May 28, 2013 [Page 5]
Internet-Draft Token Revocation November 2012
4. 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
Richer for their valuable feedback.
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
in 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
[I-D.ietf-oauth-v2-threatmodel].
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.
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 legitimate client to lose its
authorization. The malicious client does not gain further
advantages.
7. References
Lodderstedt, et al. Expires May 28, 2013 [Page 6]
Internet-Draft Token Revocation November 2012
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
[I-D.ietf-oauth-v2-threatmodel]
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.
[W3C.WD-cors-20120403]
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
Torsten Lodderstedt (editor)
Deutsche Telekom AG
Stefanie Dronia
Marius Scurtescu
Google
Additional Source: Internet Engineering Task Force
