XEP-0233: Domain-Based Service Names in XMPP SASL Negotiation

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.
Authors:Matthew Miller, Peter Saint-Andre, Joe Hildebrand
Copyright:© 1999 - 2010 XMPP Standards Foundation. SEE LEGAL NOTICES.
Type:Standards Track
Last Updated:2008-01-30

WARNING: Consideration of this document has been Deferred by the XMPP Standards Foundation. Implementation of the protocol described herein is not recommended.

Table of Contents

1. Introduction
2. Protocol
3. Security Considerations
4. IANA Considerations
5. XMPP Registrar Considerations
    5.1. Protocol Namespaces
6. XML Schema
7. Acknowledgements

    A: Document Information
    B: Author Information
    C: Legal Notices
    D: Relation to XMPP
    E: Discussion Venue
    F: Requirements Conformance
    G: Notes
    H: Revision History

1. Introduction

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.

This scenario was not addressed in RFC 3920 [1]. However, the problem can now be solved using the concept of domain-based service names as described in draft-ietf-kitten-gssapi-domain-based-names [2]. In particular, because XMPP servers typically use the Kerberos V5 ("GSSAPI") SASL mechanism as described in RFC 4752 [3], they can communicate domain-based names as Kerberos V service principal names as described in draft-ietf-kitten-krb5-gssapi-domain-based-names [4].

Therefore this document defines a method for communication of Kerberos V domain-based service names in the context of SASL negotiation by XMPP entities.

2. Protocol

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 <mechanisms/> element during SASL negotation, as specified in rfc3920bis [5]. In the case of the Kerberos V SASL mechanism, the child element is a <hostname/> element qualified by the 'urn:xmpp:tmp:domain-based-name' namespace (see Protocol Namespaces regarding issuance of one or more permanent namespaces). The <hostname/> element MUST include a 'mechanism' attribute, where the value MUST be "GSSAPI". The XML character data of the <hostname/> 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 draft-ietf-kitten-krb5-gssapi-domain-based-names (i.e., "protocol/hostname/domainname@REALM"):

Consider the example of an XMPP service whose canonical name is "example.com". A user may in fact connect to the physical machine "cm7.us.example.com". The hostname would be communicated as follows.

Example 1. Communicating the hostname

<mechanisms xmlns='urn:ietf:params:xml:ns:xmpp-sasl'>
  <hostname xmlns='urn:xmpp:tmp:domain-based-name'

The client would then attempt to obtain a ticket for the domain-based principal "xmpp/cm7.us.example.com/example.com@EXAMPLE.COM".

3. Security Considerations

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; RFC 4346 [6]) as described for XMPP in RFC 3920 and rfc3920bis. For additional security considerations, refer to draft-ietf-kitten-gssapi-domain-based-names and draft-ietf-kitten-krb5-gssapi-domain-based-names.

4. IANA Considerations

This document requires no interaction with the Internet Assigned Numbers Authority (IANA) [7].

5. XMPP Registrar Considerations

5.1 Protocol Namespaces

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 XMPP Registrar [8] shall issue a permanent namespace in accordance with the process defined in Section 4 of XMPP Registrar Function [9].

6. XML Schema

<?xml version='1.0' encoding='UTF-8'?>


  <xs:element name='hostname' type='xs:string'/>


7. Acknowledgements

Thanks to Alexey Melnikov for his comments.


Appendix A: Document Information

Series: XEP
Number: 0233
Publisher: XMPP Standards Foundation
Status: Deferred
Type: Standards Track
Version: 0.1
Last Updated: 2008-01-30
Approving Body: XMPP Council
Dependencies: XMPP Core, draft-ietf-kitten-gssapi-domain-based-names, draft-ietf-kitten-krb5-gssapi-domain-based-names
Supersedes: None
Superseded By: None
Source Control: HTML  RSS
This document in other formats: XML  PDF

Appendix B: Author Information

Matthew Miller

Email: linuxwolf@outer-planes.net
JabberID: linuxwolf@outer-planes.net

Peter Saint-Andre

Email: stpeter@jabber.org
JabberID: stpeter@jabber.org
URI: https://stpeter.im/

Joe Hildebrand

Email: jhildebr@cisco.com
JabberID: hildjj@jabber.org

Appendix C: Legal Notices


This XMPP Extension Protocol is copyright © 1999 - 2010 by the XMPP Standards Foundation (XSF).


Permission is hereby granted, free of charge, to any person obtaining a copy of this specification (the "Specification"), to make use of the Specification without restriction, including without limitation the rights to implement the Specification in a software program, deploy the Specification in a network service, and copy, modify, merge, publish, translate, distribute, sublicense, or sell copies of the Specification, and to permit persons to whom the Specification is furnished to do so, subject to the condition that the foregoing copyright notice and this permission notice shall be included in all copies or substantial portions of the Specification. Unless separate permission is granted, modified works that are redistributed shall not contain misleading information regarding the authors, title, number, or publisher of the Specification, and shall not claim endorsement of the modified works by the authors, any organization or project to which the authors belong, or the XMPP Standards Foundation.

Disclaimer of Warranty

## NOTE WELL: This Specification is provided on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, express or implied, including, without limitation, any warranties or conditions of TITLE, NON-INFRINGEMENT, MERCHANTABILITY, or FITNESS FOR A PARTICULAR PURPOSE. ##

Limitation of Liability

In no event and under no legal theory, whether in tort (including negligence), contract, or otherwise, unless required by applicable law (such as deliberate and grossly negligent acts) or agreed to in writing, shall the XMPP Standards Foundation or any author of this Specification be liable for damages, including any direct, indirect, special, incidental, or consequential damages of any character arising from, out of, or in connection with the Specification or the implementation, deployment, or other use of the Specification (including but not limited to damages for loss of goodwill, work stoppage, computer failure or malfunction, or any and all other commercial damages or losses), even if the XMPP Standards Foundation or such author has been advised of the possibility of such damages.

IPR Conformance

This XMPP Extension Protocol has been contributed in full conformance with the XSF's Intellectual Property Rights Policy (a copy of which can be found at <http://xmpp.org/extensions/ipr-policy.shtml> or obtained by writing to XMPP Standards Foundation, 1899 Wynkoop Street, Suite 600, Denver, CO 80202 USA).

Appendix D: Relation to XMPP

The Extensible Messaging and Presence Protocol (XMPP) is defined in the XMPP Core (RFC 3920) and XMPP IM (RFC 3921) 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.

Appendix E: Discussion Venue

The primary venue for discussion of XMPP Extension Protocols is the <standards@xmpp.org> 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 <editor@xmpp.org>.

Appendix F: Requirements Conformance

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".

Appendix G: Notes

1. RFC 3920: Extensible Messaging and Presence Protocol (XMPP): Core <http://tools.ietf.org/html/rfc3920>.

2. GSS-API Internationalization and Domain-Based Service Names and Name Type <http://tools.ietf.org/html/draft-ietf-kitten-gssapi-domain-based-names>. Work in progress.

3. RFC 4752: The Kerberos V5 ("GSSAPI") Simple Authentication and Security Layer (SASL) Mechanism <http://tools.ietf.org/html/rfc4752>.

4. GSS-API Domain-Based Service Names Mapping for the Kerberos V GSS Mechanism <http://tools.ietf.org/html/draft-ietf-kitten-krb5-gssapi-domain-based-names>. Work in progress.

5. rfc3920bis: proposed revisions to Extensible Messaging and Presence Protocol (XMPP): Core <http://tools.ietf.org/html/draft-ietf-xmpp-3920bis>. (work in progress)

6. RFC 4346: The Transport Layer Security (TLS) Protocol Version 1.1 <http://tools.ietf.org/html/rfc4346>.

7. 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/>.

8. The XMPP Registrar maintains a list of reserved protocol namespaces as well as registries of parameters used in the context of XMPP extension protocols approved by the XMPP Standards Foundation. For further information, see <http://xmpp.org/registrar/>.

9. XEP-0053: XMPP Registrar Function <http://xmpp.org/extensions/xep-0053.html>.

Appendix H: Revision History

Note: Older versions of this specification might be available at http://xmpp.org/extensions/attic/

Version 0.1 (2008-01-30)

Initial published version.


Version 0.0.2 (2007-12-11)

Corrected syntax.


Version 0.0.1 (2007-12-05)

First draft.