XEP-0074: Simple Access Control

WARNING: This document has been retracted by the author(s). Implementation of the protocol described herein is not recommended. Developers desiring similar functionality are advised to implement the protocol that supersedes this one (if any).

Table of Contents

1. Introduction

A Jabber travels further into the Jabber-as-Middleware world, it needs a protocol to determine "who can do what to whom". This proposal defines a protocol that enables any Jabber entity to determine the permissions of another Jabber entity, whether the context is a user JID querying a component for access, a client-to-client conversation, or a component asking another component about a request from a user.

All access control lists (ACLs) boil down to three aspects: Actor, Operation, and Target/Sink. With this in mind it becomes almost trivial to implement the basic query/response mechanism.

Example 1. A simple query

      
	<iq to="security.capulet.com"
	    from="inventory.capulet.com"
	    type="get" id="1234">
	  <acl xmlns="http://jabber.org/protocol/sac"
	       actor="juliet@capulet.com/church"
	       oper="uri://capulet.com/inventory#obtain"
	       target="poison"/>
	</iq> 
	
    

Here we have the inventory.capulet.com component querying the security component as to whether juliet@ may obtain the requested poison.

Example 2. A response to the above query

      
	<iq to="inventory.capulet.com"
	    from="security.capulet.com"
	    type="result" id="1234">
	  <acl xmlns="http://jabber.org/protocol/sac"
	       actor="juliet@capulet.com/church"
	       oper="uri://capulet.com/inventory#obtain"
	       target="poison">
	    <allowed/>
	  </acl>
	</iq> 
	
    

Unfortunately, the response is in the affirmative and the romantic tragedy follows.

2. A More Formal Tone

The <acl> element provides the container for the query. It MUST have the three attributes: actor, oper, and target.

The actor attribute is set to the Jabber ID which is attempting to perform an operation. This need not be the JID sending the acl, although it may be. Remember this is to allow for the question, "Can X do Y to Z?", which is a question anyone can ask.

The oper attribute is application-specific and refers to the operation for which a permission check is required (e.g., read/write operations). This also defines the scope of the ACL check, so the implementation is responsible for interpreting the actor and target values based on the value of the 'oper' attribute.

The target is the object which the actor is trying to perform the operation on. This MUST be a node queryable via Service Discovery [1].

Requests MUST be in the form of an empty <acl/> element with ALL the attributes specified. If not all attributes are specified, the request is incomplete and ambiguities arise; therefore the entity receving the request MUST return a "bad request" error to the sender.

Responses MUST be in one of three forms: allowed, denied, error.

The response is inserted into the <acl/> as a child element. If the response is allowed, then <allowed/> is inserted. If the JID is denied then <denied/> is returned. If there is inadequate information then <error/> is used following the standard Jabber error scheme.

Example 3. A positive response

      
	<iq to="inventory.capulet.com"
	    from="security.capulet.com"
	    type="result" id="1234">
	  <acl xmlns="http://jabber.org/protocol/sac"
	       actor="juliet@capulet.com/church"
	       oper="uri://capulet.com/inventory#obtain"
	       target="poison">
	    <allowed/>
	  </acl>
	</iq>       
	
    

Example 4. Negative response (denied)

      
	<iq to="inventory.capulet.com"
	    from="security.capulet.com"
	    type="result" id="1234">
	  <acl xmlns="http://jabber.org/protocol/sac"
	       actor="juliet@capulet.com/church"
	       oper="uri://capulet.com/inventory#obtain"
	       target="poison">
	    <denied/>
	  </acl>
	</iq> 
	
    

Example 5. Error response

      
	<iq to="inventory.capulet.com"
	    from="security.capulet.com"
	    type="error" id="1234">
	  <acl xmlns="http://jabber.org/protocol/sac"
	       actor="juliet@capulet.com/church"
	       oper="uri://capulet.com/inventory#obtain"
	       target="poison"/>
	  <error code="404">No information available</error>
	</iq> 
	
    

3. Query List of ACL operations

To obtain a list of acl operations that a jid supports, you must send an empty <query/>

Example 6. querying for list of acl operations

      
	<iq to="security.capulet.com"
	    from="inventory.capulet.com"
	    type="get" id="1234">
	  <query xmlns="http://jabber.org/protocol/sac"/>
	</iq> 
	
    

The to jid must then respond with a list of operations, if the jid supports SAC.

Example 7. response to the query

      
	<iq to="inventory.capulet.com"
	    from="security.capulet.com"
	    type="result" id="1234">
	  <query xmlns="http://jabber.org/protocol/sac">
	    <oper uri="uri://capulet.com/inventory#obtain"/>
	    <oper uri="uri://capulet.com/inventory#add"/>
	    <oper uri="uri://capulet.com/inventory#remove"/>
	  </query>
	</iq> 
	
    

4. Integrating with Service Discovery

To follow.

5. Security Considerations

To follow.

6. IANA Considerations

This document requires no interaction with the Internet Assigned Numbers Authority (IANA) [2].

7. XMPP Registrar Considerations

As a result of this document, the XMPP Registrar [3] will need to register the 'http://jabber.org/protocol/sac' namespace.

8. Open Issues

1. Add disco integration section.
2. Fill out error codes.
3. Add DTD and Schema.
4. Allow for query of all allowable operations for actor in relation to a target.
5. Investigate possible integration with pubsub.

Appendices

Appendix A: Document Information

Series: XEP
Number: 0074
Publisher: XMPP Standards Foundation
Status: Retracted
Type: Standards Track
Version: 0.2
Last Updated: 2003-10-20
Approving Body: XMPP Council
Dependencies: None
Supersedes: None
Superseded By: None
Short Name: sac
Schema: <>
Source Control: HTML
This document in other formats: XML  PDF

Appendix B: Author Information

Appendix C: Legal Notices

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

Appendix H: Revision History

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

END