Although authentication is required in order to access the XMPP network, in some situations it is desirable to require authorization in order for an authenticated entity to access certain resources on the network. For example, authorization may be required to join a Multi-User Chat (XEP-0045)  room, subscribe to a Publish-Subscribe (XEP-0060)  node, or to access other resources of interest (such as a media relay or communications gateway).
Dedicated technologies exist for authorization. One such technology is OAuth , as defined at <http://oauth.net/core/1.0/>. In the language of OAuth, a User can authorize a Consumer to access a Protected Resource that is hosted by a Service Provider; this authorization is encapsulated in a token that the User requests from the Service Provider, that the User shares with the Consumer, and that the Consumer then presents to the Service Provider in an access request.
This specification assumes that OAuth Access Tokens will be acquired outside the XMPP (i.e., via HTTP as defined in the core OAuth specification) and merely presented over XMPP when sending a protocol-specific access request.
The typical scenario is for a Consumer to request the authorization to act as a delegated authority on behalf of the User to access a Protected Resource owned by the User at a Service Provider. For example, the owner of a pubsub node could allow a remote entity to publish to that node (the single lines "---" show protocol flows over HTTP and the double lines "===" show protocol flows over XMPP):
Before presenting an access token to a Service Provider in a protocol-specific access request, a Consumer SHOULD verify that the Service Provider supports this protocol, as described under the Determining Support section of this document.
Consider the example of a User (say, <email@example.com>) who wishes to authorize a Consumer (say, an application called FindMeNow as represented by the JID <firstname.lastname@example.org>) to access the User's geolocation feed at a Service Provider called WorldGPS (as represented by a publish-subscribe node of <feeds.worldgps.tld/world-traveler>). The order of events might be as follows.
As a result, FindMeNow gets updated every time the User publishes items to his geolocation node at WorldGPS.
Steps 1-10 describe OAuth's standard HTTP flow and represent an out-band means for obtaining OAuth access tokens for use in XMPP operations.
The access request MUST include the following parameters:
The access MAY also include the "oauth_version" parameter
An example follows.
When sending an OAuth access request over XMPP, the signature method SHOULD be HMAC-SHA1. The Signature Base String SHALL be constructed from the following items:
As an example, consider the stanza shown above.
The Signature Base String would be as follows (where line endings have been added for readability and are denoted by the "\" character):
Assuming a consumer secret of 'consumersecret' and a token secret of 'tokensecret', the signature will be:
If a Service Provider rejects a Consumer's request to access a Protected Resource over XMPP, the Service Provider MUST return an XMPP stanza error. The XMPP error condition SHOULD be either <bad-request/> or <not-authorized/> and the stanza SHOULD include an OAuth-specific error condition as described in the following table.
|OAuth-Specific Condition||Generic Condition||Description|
|<duplicated-parameter/>||<bad-request/>||One of the oauth_* elements was included more than once.|
|<invalid-consumer-key/>||<not-authorized/>||The Consumer's OAuth consumer key is not valid.|
|<invalid-nonce/>||<not-authorized/>||The provided nonce is invalid; it might have already been used.|
|<invalid-signature/>||<not-authorized/>||The provided signature is invalid; the Consumer needs to confirm that the signature base string is calculated correctly.|
|<invalid-token/>||<not-authorized/>||The provided access token is invalid; it might have been revoked.|
|<missing-parameter/>||<bad-request/>||One of the required oauth_* elements is missing.|
|<token-required/>||<not-authorized/>||The Consumer did not include an OAuth access token in its request; this error condition is XMPP-specific and does not have a counterpart in the OAuth specification.|
|<unsupported-parameter/>||<bad-request/>||The <oauth/> stanza contains unknown or unsupported parameters.|
|<unsupported-signature-method/>||<bad-request/>||The specified signature method is not supported by the server.|
An example follows.
If an entity supports the protocol specified herein, it MUST advertise that fact by returning a feature of "urn:xmpp:oauth:0" in response to Service Discovery (XEP-0030)  information requests (see Protocol Namespaces regarding issuance of one or more permanent namespaces).
In order for an application to determine whether an entity supports this protocol, where possible it SHOULD use the dynamic, presence-based profile of service discovery defined in Entity Capabilities (XEP-0115) . However, if an application has not received entity capabilities information from an entity, it SHOULD use explicit service discovery instead.
Signatures generated according to the signature generation algorithm might be subject to replay attacks. However, inclusion of the XMPP "from" and "to" addresses limits these attacks to compromised servers or client-to-server connections. In addition, inclusion of the nonce value also helps to prevent replay attacks.
OAuth tokens SHOULD be sent only over TLS-encrypted client-to-server connections, and all server-to-server connections SHOULD be TLS-enabled. Additional security can be provided using appropriate methods for the end-to-end encryption of XMPP traffic, such as Current Jabber OpenPGP Usage (XEP-0027) , RFC 3923  Encrypted Session Negotiation (XEP-0116) , or End-to-End XML Streams (XEP-0246) .
This document requires no interaction with the Internet Assigned Numbers Authority (IANA) .
This specification defines the following XML namespace:
Upon advancement of this specification from a status of Experimental to a status of Draft, the XMPP Registrar  shall add the foregoing namespaces to the registry located at <https://xmpp.org/registrar/namespaces.html>, as described in Section 4 of XMPP Registrar Function (XEP-0053) .
If the protocol defined in this specification undergoes a revision that is not fully backwards-compatible with an older version, the XMPP Registrar shall increment the protocol version number found at the end of the XML namespaces defined herein, as described in Section 4 of XEP-0053.
The author gratefully acknowledges the contributions of Blaine Cook, Leah Culver, Kellan Elliott-McCrea, Seth Fitzsimmons, Nathan Fritz, Evan Henshaw-Plath, Joe Hildebrand, and Ralph Meijer to the content of this specification, as provided during the XMPP Summit held in Portland, Oregon, on July 21 and 22, 2008. Thanks also to Dave Cridland and Pedro Melo for their comments on an early draft. Seth Fitzsimmons checked many details and provided text regarding the protocol flow and error handling.
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The Extensible Messaging and Presence Protocol (XMPP) is defined in the XMPP Core (RFC 6120) and XMPP IM (RFC 6121) specifications contributed by the XMPP Standards Foundation to the Internet Standards Process, which is managed by the Internet Engineering Task Force in accordance with RFC 2026. Any protocol defined in this document has been developed outside the Internet Standards Process and is to be understood as an extension to XMPP rather than as an evolution, development, or modification of XMPP itself.
The primary venue for discussion of XMPP Extension Protocols is the <email@example.com> discussion list.
Discussion on other xmpp.org discussion lists might also be appropriate; see <http://xmpp.org/about/discuss.shtml> for a complete list.
Errata can be sent to <firstname.lastname@example.org>.
The following requirements keywords as used in this document are to be interpreted as described in RFC 2119: "MUST", "SHALL", "REQUIRED"; "MUST NOT", "SHALL NOT"; "SHOULD", "RECOMMENDED"; "SHOULD NOT", "NOT RECOMMENDED"; "MAY", "OPTIONAL".
10. The Internet Assigned Numbers Authority (IANA) is the central coordinator for the assignment of unique parameter values for Internet protocols, such as port numbers and URI schemes. For further information, see <http://www.iana.org/>.
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Note: Older versions of this specification might be available at http://xmpp.org/extensions/attic/
Changed protocol namespace from urn:xmpp:tmp:oauth to urn:xmpp:oauth:0 to conform to XMPP Registrar policies; clarified protocol flow and error handling; corrected examples.
Clarified error handling and service discovery.
More clearly specified access request format; corrected examples to incorporate nonce, timestamp, and version; modified request URL syntax to follow XML canonicalization order; changed HMAC-SHA1 from MUST to SHOULD.
Incorporated consensus reached at XMPP Summit #5: narrowed the scope to cover OAuth only, specified that HTTP is used except for sending the access request via XMPP, corrected signature generation algorithm, specified security considerations, and removed invitation and account registration use cases.
Changed data forms usage to semantic XML format (except for in-band registration).
Generalized to cover authorization tokens; added use cases for pubsub node subscriptions and XMPP account registration.
Initial published version.