XEP-0356: Privileged Entity

Abstract:This specification provides a way for XMPP entities to have a privileged access to some other entities data
Author:Jérôme Poisson
Copyright:© 1999 – 2017 XMPP Standards Foundation. SEE LEGAL NOTICES.
Status:Experimental
Type:Standards Track
Version:0.2
Last Updated:2015-03-23

WARNING: This Standards-Track document is Experimental. Publication as an XMPP Extension Protocol does not imply approval of this proposal by the XMPP Standards Foundation. Implementation of the protocol described herein is encouraged in exploratory implementations, but production systems are advised to carefully consider whether it is appropriate to deploy implementations of this protocol before it advances to a status of Draft.

Table of Contents


1. Introduction
2. Requirements
3. Glossary
4. Accessing Roster
    4.1. Server Allows Roster Access
    4.2. Server Advertises Entity Of Allowed Permission
    4.3. Privileged Entity Manage Roster
5. Message Permission
    5.1. Authorizing Messages
    5.2. Advertising Permission
    5.3. Sending Messages
6. Presence Permission
    6.1. Managed Entity Presence
    6.2. Advertising Permission
    6.3. Server Send presence informations
    6.4. Roster Presence
    6.5. Advertising Permission
    6.6. Privileged Entity Receive Roster Presences
7. Business Rules
8. Security Considerations
9. IANA Considerations
10. XMPP Registrar Considerations
    10.1. Protocol Namespaces
    10.2. Protocol Versioning
11. XML Schema
12. Acknowledgements

Appendices
    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

XMPP components are used for long through Jabber Component Protocol (XEP-0114) [1], but are quite limited: they have a restricted access to other entities data, similar to what a client can do. This is sufficient for components like gateways, but very limiting for more complex components like a PubSub service. The goal of this XEP is to allow a component or any entity to have a "privileged" status, and access some other entity data with the same privileges than the entity itself, that means manage an entity roster on its behalf, send <message/> or receive <presence/> stanzas in the name of the server.

Privileged entities have numerous advantages, including:

Privileged entity has been created with the main goal to create an external, server agnostic, PEP service. It is restricted to only a couple of features, see Acknowledgements section for more details.

This XEP is complementary to Namespace Delegation (XEP-0355) [3] (and works in a similar way), although they can be used together or separately. To build something like an external PEP service, it is necessary to use both XEPs.

2. Requirements

A privileged entity must be able to do what a PEP service can do and to access roster, so it must be able to (according to configuration):

The privilege mechanism MUST be totally transparent for the managed entities.

3. Glossary

4. Accessing Roster

4.1 Server Allows Roster Access

Roster access is granted in the server configuration. Roster access can have 4 types:

4.2

Once a privileged entity is authenticated and stream is started, the server send it a <message/> stanza with a <privilege/> elements which MUST have the namespace 'urn:xmpp:privilege:1'. This element contains <perm/> elements which MUST contain a 'access' attribute of the value "roster" and a 'type' attribute which must correspond to the type configured as specified in "Server Allows Roster Access" section

Example 1. Server Advertises Roster Privilege

<message from='capulet.net' to='pubub.capulet.lit' id='12345'>
    <privilege xmlns='urn:xmpp:privilege:1'>
        <perm access='roster' type='both'/>
    </privilege>
</message>

Here pubsub.capulet.lit is allowed to do get and set operations on all entities managed by capulet.lit

4.3 Privileged Entity Manage Roster

Doing a get or set operation on the roster of a managed entity is done in the usual way (as described in RFC 6121 [4] section 2), except that the 'to' attribute is set to the attribute of the managed entity. The server MUST check that the privileged entity has right to get or set the roster of managed entity, and MUST return a <forbidden/> error if it is not the case:

Example 2. Privileged Entity Get Managed Entity Roster

<iq id='roster1'
    from='pubsub.capulet.lit'
    to='juliet@example.com'
    type='get'
    id='roster1'>
        <query xmlns='jabber:iq:roster'/>
</iq>

The server then answers normally, as it would have done to the managed entity:

Example 3. Server Answers To Privileged Entity

<iq id='roster1'
    from='juliet@example.com'
    to='pubsub.capulet.net'
    type='result'>
    <query xmlns='jabber:iq:roster' ver='ver7'>
        <item jid='nurse@example.com'/>
        <item jid='romeo@example.net'/>
    </query>
</iq>

5. Message Permission

5.1 Authorizing Messages

In some cases, it can be desirable to send notifications (e.g. PEP service), so the privileged entity must be able to send <message/> stanzas. This is allowed in server configuration in the same way as for roster permission. The permission type can have the following values:

A privileged entity can then send message on the behalf either of the server or of a bare JID of an entity managed by the server (i.e. a bare jid with the same domain as the server), using Stanza Forwarding (XEP-0297) [5]. The <forwarded/> element MUST be a child of a <privilege/> element with a namespace of 'urn:xmpp:privilege:1', with the following restriction:

  1. forwarded <message/> 'from' attribute MUST be a bare JID from the server, no resource is allowed

If this rule is violated, the server MUST return a <message/> error with condition <forbidden/>, as in RFC 6120 [6] section 8.3.3.4.

5.2

Server advertises "message" permission in the same way as for "roster" permission, except that 'access' attribute has the value of "message", and the 'type' attribute as a value of 'outgoing':

Example 4. Server Advertises Roster And Message Privileges

<message from='capulet.net' to='pubub.capulet.lit' id='54321'>
    <privilege xmlns='urn:xmpp:privilege:1'>
        <perm access='roster' type='both'/>
        <perm access='message' type='outgoing'/>
    </privilege>
</message>

5.3 Sending Messages

Now that pubsub.capulet.lit is allowed, it can send messages using <forwarded/> elements.

Example 5. privileged entity send a notificaction message

<message from='pubsub.capulet.lit' to='capulet.lit' id='notif1'>
    <privilege xmlns='urn:xmpp:privilege:1'>
        <forwarded xmlns='urn:xmpp:forward:0'>
            <message from='juliet@capulet.lit'
                id='foo'
                to='romeo@montague.lit/orchard'
                xmlns='jabber:client'>
                <event xmlns='http://jabber.org/protocol/pubsub#event'>
                    <items node='http://jabber.org/protocol/tune'>
                        <item>
                            <tune xmlns='http://jabber.org/protocol/tune'>
                                <artist>Gerald Finzi</artist>
                                <length>255</length>
                                <source>Music for "Love's Labors Lost" (Suite for small orchestra)</source>
                                <title>Introduction (Allegro vigoroso)</title>
                                <track>1</track>
                            </tune>
                        </item>
                    </items>
                </event>
                <delay xmlns='urn:xmpp:delay' stamp='2014-11-25T14:34:32Z'/>
            </message>
        </forwarded>
    </privilege>
</message>

The server sees that forwarded message 'from' attribute (juliet@capulet.lit) is a bare JID of the server, and that outgoing message permission was granted; it can now send the notification:

Example 6. server sends the notification as if it was originating from him

<message from='juliet@capulet.lit'
    id='bar'
    to='romeo@montague.lit/orchard'>
    <event xmlns='http://jabber.org/protocol/pubsub#event'>
        <items node='http://jabber.org/protocol/tune'>
            <item>
                <tune xmlns='http://jabber.org/protocol/tune'>
                    <artist>Gerald Finzi</artist>
                    <length>255</length>
                    <source>Music for "Love's Labors Lost" (Suite for small orchestra)</source>
                    <title>Introduction (Allegro vigoroso)</title>
                    <track>1</track>
                </tune>
            </item>
        </items>
    </event>
    <delay xmlns='urn:xmpp:delay' stamp='2014-11-25T14:34:32Z'/>
</message>

6. Presence Permission

6.1 Managed Entity Presence

It can be often desirable for a privileged entity to have presence information of the managed entities (e.g. to know when to send them notificiations). As privileges must be transparent for the managed entity, this presence has to be sent by the server without modifying managed entity roster.

This is allowed in server configuration in the same way as for roster and message permissions. The "presence" type can have the following values:

If the privilege is granted, the server MUST use a directed presence from the full jid of the managed entity, to the privileged entity, as specified in RFC 6121 [4] section 4.6, on the behalf of managed entity each time its presence information change.

Only presences with no 'type' attribute or with a 'type' attribute with the value "unavailable" are transmitted to the privileged entity, the server MUST NOT transmit <presence/> stanza of any other type.

6.2

Server advertises "presence" permission in the same way as for "roster" or "message" permissions, except that 'access' attribute has the value of "presence", and the 'type' attribute has a value of "managed_entity"

6.3 Server Send presence informations

Once the "presence" permission is granted, the server send presence informations:

Example 7. server receives new presence from Juliet

<presence from='juliet@capulet.lit/balcony'
          id='presence1'
          xml:lang='en'>
    <show>chat</show>
    <status>Staying on the balcony</status>
</presence>

Example 8. server redirects presence to privileged entity

<presence from='juliet@capulet.lit/balcony'
          to='pubsub.capulet.lit'
          id='presence1'
          xml:lang='en'>
    <show>chat</show>
    <status>Staying on the balcony</status>
</presence>

6.4 Roster Presence

In addition to "managed entity presence", a privileged entity may need to know when a contact in managed entity roster is online (for example, it's necessary for a PEP service because of the presence default access model).

As for other permissions, the access is granted in server's configuration, but there is an additional restriction: the privileged entity MUST have read permission on roster namespace (i.e. 'type' attribute in allowed <perm> of access roster MUST have a value of either get or both).

If the privilege is granted, the server MUST send to the privileged entity every presence information with no 'type' attribute or with a 'type' with a value of 'unavailable' that the privileged entity is receiving or would receive if it were available. It do it in the same way as for managing entity by using directed <presence/> from the full jid of the entity from which presence information has changed, to the privileged entity. If the managed entity is unavailable but the privileged entity is available, the server MUST send <presence/> stanza to the later anyway.

Having "roster" type for "presence" permission imply that you have also implicitly "managed_entity" type.

The server MUST reject the permission if the privileged entity doesn't have read permission on roster namespace.

Note: this permission should be given carefully, as it gives access to presence of potentially a lot of entities to the privileged entity (see security considerations).

6.5

Server advertises roster "presence" permission in the same way as for other permissions, except that the 'access' attribute has the value of "presence", and the 'type' attribute has a value of "roster"

Example 9. Server Advertises Roster, Message, Managed Entity Presence and Roster Presence Privileges

<message from='capulet.net' to='pubub.capulet.lit' id='54321'>
    <privilege xmlns='urn:xmpp:privilege:1'>
        <perm access='roster' type='both'/>
        <perm access='message'/>
        <perm access='presence' type='roster'/>
    </privilege>
</message>

Note the presence of roster permission request.

6.6 Privileged Entity Receive Roster Presences

Example 10. server receives new presence from Romeo, which is in Juliet's roster

<presence from='romeo@montaigu.lit/orchard'/>

Example 11. server sends the presence as usually, but also to the privileged entity

<presence from='romeo@montaigu.lit/orchard'
          to='juliet@capulet.lit'/>
<presence from='romeo@montaigu.lit/orchard'
          to='pubsub.capulet.lit'/>

7. Business Rules

  1. For "presence" access, if a privileged entity is connected after first <presence/> stanzas have been received, the server MUST send it all the <presence/> stanzas with no 'type' attribute it would have had if it was connected first (in other words: all the presences informations for connected entities it has access to).
  2. For "presence" access, if a privileged entity is supposed to received several time the same <presence/> stanza, the server SHOULD send it only once. For example: if pubsub.capulet.lit has a "presence" access with a "roster" type for capulet.lit, and juliet@capulet.lit and nurse@capulet.it both have romeo@montague.lit in their roster. When romeo is available, pubsub.capulet.lit shoud have its <presence/> stanza only once (instead of 2 times).

8. Security Considerations

  1. Privileged entitiy has access to sensitive data, and can act as the server itself, permissions should be granted carefuly, only if you absolutely trust the entity.
  2. Roster presence is particulary sensitive, because presence informations of whole rosters are shared.
  3. Generaly, the server MUST NOT allow the privileged entity to do anything that the managed entity could not do.

9. IANA Considerations

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

10. XMPP Registrar Considerations

10.1 Protocol Namespaces

The XMPP Registrar [8] includes 'urn:xmpp:privilege:1' in its registry of protocol namespaces (see <https://xmpp.org/registrar/namespaces.html>).

10.2 Protocol Versioning

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.

11. XML Schema

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

<xs:schema
    xmlns:xs='http://www.w3.org/2001/XMLSchema'
    targetNamespace='urn:xmpp:privilege:1'
    xmlns='urn:xmpp:privilege:1'
    elementFormDefault='qualified'>

  <xs:element name='privilege'>
      <xs:complexType>
          <xs:element name='perm'
                      maxOccurs='unbounded'>
              <xs:complexType>
                  <xs:attribute name='access' use='required' type='xs:string'/>
                      <xs:simpleType base='xs:NMTOKEN'>
                          <xs:enumeration value='roster'/>
                          <xs:enumeration value='message'/>
                          <xs:enumeration value='presence'/>
                      </xs:simpleType>
                  <xs:attribute name='type' use='required'>
                      <xs:simpleType base='xs:NMTOKEN'>
                          <xs:enumeration value='none'/>
                          <xs:enumeration value='get'/>
                          <xs:enumeration value='set'/>
                          <xs:enumeration value='both'/>
                          <xs:enumeration value='outgoing'/>
                          <xs:enumeration value='managed_entity'/>
                          <xs:enumeration value='roster'/>
                      </xs:simpleType>
                  </xs:attribute>
              </xs:complexType>
          </xs:element>
      </xs:complexType>
</xs:element>

</xs:schema>

12. Acknowledgements

Thanks to Sergey Dobrov, Dave Cridland, Steven Lloyd Watkin, Lance Stout, Johannes Hund, Kurt Zeilenga and Kevin Smith for their feedbacks. Thanks to Adrien Cossa for his typos/style corrections.

Privileged entity was initialy written to be a generic identity based access control (IBAC) which allows an entity to access sensitive data. After a discussion on standard mailing list, it has been decided to restrict the current XEP to immediate needs to build an external PEP service, and to implement separately an Attribute Based Access Control (ABAC) which is more modern, generic and flexible. This XEP is still interesting for being easy to implement and doing the job.

Appendices

Appendix A: Document Information

Series: XEP
Number: 0356
Publisher: XMPP Standards Foundation
Status: Experimental
Type: Standards Track
Version: 0.2
Last Updated: 2015-03-23
Approving Body: XMPP Council
Dependencies: XMPP Core
Supersedes: None
Superseded By: None
Short Name: NOT_YET_ASSIGNED
Source Control: HTML
This document in other formats: XML  PDF

Appendix B: Author Information

Jérôme Poisson

Email: goffi@goffi.org
JabberID: goffi@jabber.fr

Appendix C: Legal Notices

Copyright

This XMPP Extension Protocol is copyright © 1999 – 2017 by the XMPP Standards Foundation (XSF).

Permissions

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 <https://xmpp.org/about/xsf/ipr-policy> or obtained by writing to XMPP Standards Foundation, P.O. Box 787, Parker, CO 80134 USA).

Appendix D: Relation to XMPP

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.

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. XEP-0114: Jabber Component Protocol <https://xmpp.org/extensions/xep-0114.html>.

2. XEP-0163: Personal Eventing Protocol <https://xmpp.org/extensions/xep-0163.html>.

3. XEP-0355: Namespace Delegation <https://xmpp.org/extensions/xep-0355.html>.

4. RFC 6121: Extensible Messaging and Presence Protocol (XMPP): Instant Messaging and Presence <http://tools.ietf.org/html/rfc6121>.

5. XEP-0297: Stanza Forwarding <https://xmpp.org/extensions/xep-0297.html>.

6. RFC 6120: Extensible Messaging and Presence Protocol (XMPP): Core <http://tools.ietf.org/html/rfc6120>.

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 <https://xmpp.org/registrar/>.

Appendix H: Revision History

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

Version 0.2 (2015-03-23)

Several updates according to feedbacks + review:

(jp)

Version 0.1 (2015-01-27)

Initial published version approved by the XMPP Council.

(XEP Editor (mam))

Version 0.0.4 (2014-12-18)

(jp)

Version 0.0.3 (2014-11-13)

(jp)

Version 0.0.2 (2014-09-17)

(jp)

Version 0.0.1 (2014-05-09)

First draft.

(jp)

END