Automatic reconnection after spurious disconnection is a must-have feature in modern IM applications. One way of providing this feature is storing user login information on disk for reuse. However, plaintext storage of passwords is inherently insecure, while protecting the XMPP password with a master-password is inconvenient for the end-user. With a token-based authentication mechanism, the user only has to provide login information once, for the initial connection to the XMPP server, and can later rely on the application's automatic use of tokens for subsequent reconnections.
Moreover, while reconnecting to the XMPP server, the client usually has to go through the same long process of SASL challenge-response exchange which may lead to a noticably long reconnection time, especially while using SCRAM-based mechanisms. Providing a token to the XMPP server is both secure and doesn't require multiple challenge-response roundtrips, therefore might significantly speed up reconnection times.
This extension requires the client application to authenticate to the XMPP server using a regular XMPP authentication mechanism like SCRAM-SHA-1 at least once. After that, the following authentications may be done using X-OAUTH SASL mechanism with a token obtained from the server.
|Access token||These are short lived tokens whose grants aren't tracked by the server (i.e. there's no need to store anything in a database). Access tokens can be used as a payload for the X-OAUTH authentication mechanism and grant access to the system. Access tokens can't be revoked. An access token is valid only until its expiry date is reached.|
|Refresh token||These are longer lived tokens which are tracked by the server, therefore require persistent storage. Refresh tokens can be used as a payload for the X-OAUTH authentication mechanism and grant access to the system, as well as result in a new set of tokens being returned upon successful authentication. Refresh tokens can be revoked. A refresh token is valid until it has expired, unless it has been revoked. On revocation, it immediately becomes invalid. As the server stores information about granted tokens, it can also persistently mark them as revoked.|
While only two token types have been described above, implementations might use other token types for specific purposes. For example, a particular token type could limit the access privileges of a user logged into the system or denote an affiliation with a Multi User Chat room. None of such capability grants are subject of this specification, though.
This section is informal. The token formats described below are used in one of the experimental implementations, but are not proposed as standard. If such a standard turns out to be required, then JSON Web Tokens might be a viable format to adopt.
All tokens are exchanged as Base64 encoded binary data. Serialization format of the token before encoding with Base64 is dependent on its type. Common parts in every token are
EXPIRES_AT is a timestamp saying when given token will expire.
\0 stands for the ASCII null character (i.e. byte 0). Text in single quotes (
'example') is literal.
ALL_CAPS denote parameters.
Example, please note the line break was added only for readability:
Example, please note the line break was added only for readability:
After authentication with some other mechanism like SCRAM-SHA-1, a client may request a token from the server by sending following iq get to its own bare JID:
In this situation server will respond with a new refresh token which SHOULD be used in future authentication.
A classical authentication is required in order to be able to use a token-based authentication later.
The DATA field in token is relevant only to the XMPP server supporting this extension.
The tokens MUST be exhanged over a secured/encrypted C2S stream (via TLS, for example).
This document requires no interaction with the Internet Assigned Numbers Authority (IANA) .
This document requires no interaction with the XMPP Registrar .
REQUIRED for protocol specifications.
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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.
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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".
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Note: Older versions of this specification might be available at http://xmpp.org/extensions/attic/
Removed mention of OAuth from Abstract; removed mention of DIGEST-MD5.