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0.2

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git-svn-id: file:///home/ksmith/gitmigration/svn/xmpp/trunk@4234 4b5297f7-1745-476d-ba37-a9c6900126ab
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Peter Saint-Andre 2010-06-11 15:38:31 +00:00
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xep-0233.xml
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@ -10,14 +10,14 @@
<abstract>This specification defines a method by which a connection manager associated with an XMPP server can inform a connecting client about its domain-based service name.</abstract>
&LEGALNOTICE;
<number>0233</number>
<status>Deferred</status>
<status>Experimental</status>
<type>Standards Track</type>
<sig>Standards</sig>
<approver>Council</approver>
<dependencies>
<spec>XMPP Core</spec>
<spec>draft-ietf-kitten-gssapi-domain-based-names</spec>
<spec>draft-ietf-kitten-krb5-gssapi-domain-based-names</spec>
<spec>RFC 5178</spec>
<spec>RFC 5179</spec>
</dependencies>
<supersedes/>
<supersededby/>
@ -25,6 +25,12 @@
&linuxwolf;
&stpeter;
&hildjj;
<revision>
<version>0.2</version>
<date>2010-06-10</date>
<initials>psa</initials>
<remark><p>Expanded use beyond Kerberos; updated namespace; corrected schema; updated references.</p></remark>
</revision>
<revision>
<version>0.1</version>
<date>2008-01-30</date>
@ -46,13 +52,14 @@
</header>
<section1 topic='Introduction' anchor='intro'>
<p>In certain kinds of XMPP deployments, multiple connection managers associated with the XMPP server may be used to handle requests from connecting clients. When such an architecture is used in environments that make use of Kerberos V and negotiation of Simple Authentication and Security Layer (SASL) over XMPP, the connection manager may need to give the client additional information about its principal so that the client can obtain a proper ticket for authentication.</p>
<p>This scenario was not addressed in &rfc3920;. However, the problem can now be solved using the concept of domain-based service names as described in &kittenspn;. In particular, because XMPP servers typically use the Kerberos V5 ("GSSAPI") SASL mechanism as described in &rfc4752;, they can communicate domain-based names as Kerberos V service principal names as described in &kittenspnkrb5;.</p>
<p>Therefore this document defines a method for communication of Kerberos V domain-based service names in the context of SASL negotiation by XMPP entities.</p>
<p>In certain kinds of XMPP deployments, multiple connection managers associated with the XMPP server can be used to handle requests from connecting clients. In such an architecture, the connection manager might need to communicate the hostname to which the client has connected, or information about alternative connection manager.</p>
<p>This is especially true in environments that make use of Kerberos V and negotiation of Simple Authentication and Security Layer (SASL) over XMPP, because the client might need additional information about the Kerberos principal so that it can obtain a proper ticket for authentication.</p>
<p>This scenario was not addressed in &rfc3920;. However, the problem can now be solved using the concept of domain-based service names as described in &rfc5178;. In particular, because XMPP servers typically use the Kerberos V5 ("GSSAPI") SASL mechanism as described in &rfc4752;, they can communicate domain-based names as Kerberos V service principal names as described in &rfc5179;.</p>
<p>Therefore this document defines a method for communication of authentication hostnames (especially Kerberos V domain-based service names) in the context of SASL negotiation by XMPP entities.</p>
</section1>
<section1 topic='Protocol' anchor='proto'>
<p>When a connection manager associated with an XMPP server needs to communicate additional information about its service principal name to a connecting client, it can do so by including a child element of the &lt;mechanisms/&gt; element during SASL negotation, as specified in &rfc3920bis;. In the case of the Kerberos V SASL mechanism, the child element is a &lt;hostname/&gt; element qualified by the 'urn:xmpp:tmp:domain-based-name' namespace &NSNOTE;. The &lt;hostname/&gt; element MUST include a 'mechanism' attribute, where the value MUST be "GSSAPI". The XML character data of the &lt;hostname/&gt; element shall specify the fully-qualified name of the connection manager (known as the hostname). The client then generates a domain-based service name from the provided hostname, following the format specified in <cite>draft-ietf-kitten-krb5-gssapi-domain-based-names</cite> (i.e., "protocol/hostname/domainname@REALM"):</p>
<section1 topic='Use with Kerberos' anchor='kerberos'>
<p>When a connection manager associated with an XMPP server needs to communicate additional information about its service principal name to a connecting client, it can do so by including a child element of the &lt;mechanisms/&gt; element during SASL negotation, as specified in &rfc3920bis;. In the case of the Kerberos V SASL mechanism, the child element is a &lt;hostname/&gt; element qualified by the 'urn:xmpp:domain-based-name:0' namespace &NSNOTE;. In the context of Kerberos, the &lt;hostname/&gt; element MUST include a 'mechanism' attribute, where the value MUST be "GSSAPI". The XML character data of the &lt;hostname/&gt; element shall specify the fully-qualified name of the connection manager (known as the hostname). The client then generates a domain-based service name from the provided hostname, following the format specified in <cite>RFC 5179</cite> (i.e., "protocol/hostname/domainname@REALM"):</p>
<ul>
<li>The <strong>protocol</strong> string MUST be "xmpp"</li>
<li>The <strong>hostname</strong> string MUST be the XML character data of the &lt;hostname/&gt; element</li>
@ -65,15 +72,29 @@
<mechanism>GSSAPI</mechanism>
<mechanism>DIGEST-MD5</mechanism>
<required/>
<hostname xmlns='urn:xmpp:tmp:domain-based-name'
<hostname xmlns='urn:xmpp:domain-based-name:0'
mechanism='GSSAPI'>cm7.us.example.com</hostname>
</mechanisms>
]]></example>
<p>The client would then attempt to obtain a ticket for the domain-based principal "xmpp/cm7.us.example.com/example.com@EXAMPLE.COM".</p>
</section1>
<section1 topic='Non-Kerberos Use Cases' anchor='other'>
<p>This protocol can also be used to communicate connection manager hostnames outside the context of Kerberos. In this case, the &lt;hostname/&gt; element will not include the 'mechanism' attribute, and multiple instances of the &lt;hostname/&gt; element can be included. An example follows.</p>
<example caption="Communicating hostnames"><![CDATA[
<mechanisms xmlns='urn:ietf:params:xml:ns:xmpp-sasl'>
<mechanism>GSSAPI</mechanism>
<mechanism>DIGEST-MD5</mechanism>
<required/>
<hostname xmlns='urn:xmpp:domain-based-name:0'>cm3.us.example.com</hostname>
<hostname xmlns='urn:xmpp:domain-based-name:0'>cm5.us.example.com</hostname>
<hostname xmlns='urn:xmpp:domain-based-name:0'>cm9.us.example.com</hostname>
</mechanisms>
]]></example>
</section1>
<section1 topic='Security Considerations' anchor='security'>
<p>The communication of hostnames during SASL negotiation is not known to introduce new security vulnerabilities. Communication of hostnames SHOULD NOT occur until after the underlying channel has been secured using Transport Layer Security (TLS; &rfc4346;) as described for XMPP in <cite>RFC 3920</cite> and <cite>rfc3920bis</cite>. For additional security considerations, refer to <cite>draft-ietf-kitten-gssapi-domain-based-names</cite> and <cite>draft-ietf-kitten-krb5-gssapi-domain-based-names</cite>.</p>
<p>The communication of hostnames during SASL negotiation is not known to introduce new security vulnerabilities. Communication of hostnames SHOULD NOT occur until after the underlying channel has been secured using Transport Layer Security (TLS; &rfc5246;) as described for XMPP in <cite>RFC 3920</cite> and <cite>rfc3920bis</cite>. For additional security considerations, refer to <cite>RFC5178</cite> and <cite>RFC 5179</cite>.</p>
</section1>
<section1 topic='IANA Considerations' anchor='iana'>
@ -81,8 +102,15 @@
</section1>
<section1 topic='XMPP Registrar Considerations' anchor='registrar'>
<section2 topic='Protocol Namespaces' anchor='ns'>
<p>Until this specification advances to a status of Draft, its associated namespace shall be "urn:xmpp:tmp:domain-based-name"; upon advancement of this specification, the &REGISTRAR; shall issue a permanent namespace in accordance with the process defined in Section 4 of &xep0053;.</p>
<section2 topic='Protocol Namespaces' anchor='registrar-ns'>
<p>This specification defines the following XML namespace:</p>
<ul>
<li>urn:xmpp:domain-based-name:0:0</li>
</ul>
<p>Upon advancement of this specification from a status of Experimental to a status of Draft, the &REGISTRAR; shall add the foregoing namespace to the registry located at &NAMESPACES;, as described in Section 4 of &xep0053;.</p>
</section2>
<section2 topic='Protocol Versioning' anchor='registrar-versioning'>
&NSVER;
</section2>
</section1>
@ -92,18 +120,26 @@
<xs:schema
xmlns:xs='http://www.w3.org/2001/XMLSchema'
targetNamespace='urn:xmpp:tmp:domain-based-name'
xmlns='urn:xmpp:tmp:domain-based-name'
targetNamespace='urn:xmpp:domain-based-name:0'
xmlns='urn:xmpp:domain-based-name:0'
elementFormDefault='qualified'>
<xs:element name='hostname' type='xs:string'/>
<xs:element name='hostname'>
<xs:complexType>
<xs:simpleContent>
<xs:extension base='xs:string'>
<xs:attribute name='mechanism' type='xs:NMTOKEN' use='optional'/>
</xs:extension>
</xs:simpleContent>
</xs:complexType>
</xs:element>
</xs:schema>
]]></code>
</section1>
<section1 topic='Acknowledgements' anchor='ack'>
<p>Thanks to Alexey Melnikov for his comments.</p>
<p>Thanks to Owen Friel, Shane Hannon, Seamus Kerrigan, and Alexey Melnikov for their comments.</p>
</section1>
</xep>