XEP-0355: Namespace Delegation

Abstract
This specification provides a way for XMPP server to delegate treatments for a namespace to an other entity
Author
Jérôme Poisson
Copyright
© 1999 – 2021 XMPP Standards Foundation. SEE LEGAL NOTICES.
Status

Experimental

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.
Type
Standards Track
Version
0.5 (2021-10-15)
Document Lifecycle
  1. Experimental
  2. Proposed
  3. Stable
  4. Final

1. Introduction

Some XMPP features must be offered by the server itself, or can't be available, that's the case of Personal Eventing Protocol (XEP-0163) [2] which is used in several places (e.g. bookmarks storage). But it can be desirable to use an external entity to manage some of these features, because it implements things that the server don't, or because it uses a special implementation useful in a particular case. Some people may also want to decentralize a feature on an entity under their control. This XEP try to solve these cases.
Additionaly, a method to do generic treatments (independent of server) on stanza is also provided.

This XEP is complementary to Privileged Entity (XEP-0356) [3] (and works in a similar way), although they can be used together or separately.

Here are some use cases of namespace delegation:

2. Requirements

Namespace delegation can be used in two modes:

In admin mode, the managing entity manages stanza of the delegated namespace for all users registered on the server. The namespace delegation MUST be totally transparent for the managed entities.

In client mode, a managing entity MUST have an explicit authorization for any namespace he wants to use. Client SHOULD be able to check and revoke granted permissions, and if it's not possible, permissions MUST be revoked after a disconnection.

3. Glossary

4. Admin Mode Use Cases

4.1 Server Allows Namespaces Delegations

Namespaces delegations are granted in the server configuration. Only <iq/> stanza namespaces can be delegated.

A feature is delegated using:

  1. its namespace: e.g. 'urn:xmpp:mam:2'
  2. zero or more filtering attribute (attributes which must be present in the initial <iq/> child element): e.g. 'node'
  3. the jid of the managing entity: e.g. 'managing.capulet.lit'

4.2 Delegation Request Use Case

Once the managing entity is authenticated and stream is started, the server send it a <message/> stanza with a <delegation/> elements which MUST have the 'urn:xmpp:delegation:2' namespace. This element contains <delegated/> elements which MUST contain a 'namespace' attribute indicating the delegated namespace. If there is additional attribute filtering, the <delegated/> can have children <attribute/> elements which MUST contain a 'name' attribute with the name of the filtering attribute.

Example 1. server advertise delegated namespaces
<message from='capulet.lit' to='pubub.capulet.lit' id='12345'>
    <delegation xmlns='urn:xmpp:delegation:2'>
        <delegated namespace='urn:xmpp:mam:2'>
            <attribute name='node' />
        </delegated>
        <delegated namespace='http://jabber.org/protocol/pubsub'/>
    </delegation>
</message>

Here pubsub.capulet.lit will received all stanzas of pubsub namespace sent to capulet.lit. It will also receive MAM stanzas, but only if the 'node' attribute is present in <query/>.

4.3 Server Forwards Delegated <iq/> Stanza

When a server receives a stanza for a delegated namespace which is either directed to him (no 'to' attribute, or 'to' attribute with its own JID), or directed to any bare jid (and only bare jid) that it manages (i.e. the domainpart is a domain handled by the server where delegation is activated), it MUST forwards it to the managing entity:

Example 2. Juliet sends her mood to her server via PEP
<iq from='juliet@capulet.lit/balcony'
    id='pep1'
    type='set'>
    <pubsub xmlns='http://jabber.org/protocol/pubsub'>
        <publish node='http://jabber.org/protocol/mood'>
        <item>
            <mood xmlns='http://jabber.org/protocol/mood'>
                <annoyed/>
                <text>curse my nurse!</text>
            </mood>
        </item>
        </publish>
    </pubsub>
</iq>

The server gets this stanza, sees that this namespace is delegated to pubsub.capulet.lit, so it forwards it.

To forward, an <iq/> stanza of type "set" is used which contain a <delegation/> element (with namespace 'urn:xmpp:delegation:2') which in turn contain a <forwarded/> element encapsulating the initial stanza, according to Stanza Forwarding (XEP-0297) [1]:

Example 3. Server Delegates The Stanza To pubsub.capulet.lit
<iq from='capulet.lit'
    to='pubsub.capulet.lit'
    id='delegate1'
    type='set'>
    <delegation xmlns='urn:xmpp:delegation:2'>
        <forwarded xmlns='urn:xmpp:forward:0'>
            <iq from='juliet@capulet.lit/balcony'
                id='pep1'
                type='set'
                xmlns='jabber:client'>
                <pubsub xmlns='http://jabber.org/protocol/pubsub'>
                    <publish node='http://jabber.org/protocol/mood'>
                    <item>
                        <mood xmlns='http://jabber.org/protocol/mood'>
                            <annoyed/>
                            <text>curse my nurse!</text>
                        </mood>
                    </item>
                    </publish>
                </pubsub>
            </iq>
        </forwarded>
    </delegation>
</iq>

The managing entity replies to the stanza by encapsulating its <iq/> result in the same way:

Example 4. pubsub.capulet.lit Replies To Juliet
<iq from='pubsub.capulet.lit'
    to='capulet.lit'
    id='delegate1'
    type='result'>
    <delegation xmlns='urn:xmpp:delegation:2'>
        <forwarded xmlns='urn:xmpp:forward:0'>
            <iq to='juliet@capulet.lit/balcony'
                id='pep1'
                type='result'
                xmlns='jabber:client'>
                <pubsub xmlns='http://jabber.org/protocol/pubsub' />
            </iq>
        </forwarded>
    </delegation>
</iq>

Then the server MUST decapsulate the <iq/> result, MUST insure that the 'to' and the 'from' attribute corresponds to respectively the 'from' and the 'to' attributes of the initial stanza, MUST insure that the 'id' attribute of the decapsulated stanza is the same as the initial 'id' attribute and that 'type' is "result". If everything is alright, it can send the decapsulated stanza to Juliet.

If the forwarded result from managing entity is bad (i.e. wrong 'to', 'from', 'id' or 'result' attributes), the server MUST send an <iq/> error with condition <service-unavailable/> to managed entity, and MAY close the connexion with managing entity.

Example 5. capulet.lit Replies To Juliet
<iq to='juliet@capulet.lit/balcony'
    id='pep1'
    type='result'>
    <pubsub xmlns='http://jabber.org/protocol/pubsub' />
</iq>

The workflow is fully transparent for Juliet.

N.B.₁: If the server encounter a delegated namespace and the managing entity is not available, it MUST return an <iq/> stanza of type "error" with an error condition of <service-unavailable/>

N.B.₂: Similarly, if the managing entity return an <iq/> stanza of type "error", the server must return itself an <iq/> stanza of type "error" with an error condition of <service-unavailable/>

N.B.₃: If the server encounter a delegated namespace but the filtering attribute does not match, it MUST follow its normal behaviour, i.e. it must follow the same behaviour it would have had if the namespace was not delegated at all

4.3.1 Stanzas from managing entity

If a stanza is sent by the managing entity on a managed namespace, the server MUST NOT forward it. This way, the managing entity can use privileged entity to do specific treatments, a kind of universal plugin (i.e. working with all servers implementing Namespace Delegation (XEP-0355) [4] and Privileged Entity (XEP-0356) [3]).

In the following examples, juliet@capulet.lit has its "jabber:iq:roster" namespace delegated to filter.capulet.lit. filter.capulet.lit is a server agnostic component which filters allowed entities (which can be added to a roster), and sort them in enforced groups.

Example 6. Juliet adds Romeo to her roster
<iq from='juliet@capulet.lit/balcony'
          id='roster1'
          type='set'>
    <query xmlns='jabber:iq:roster'>
        <item jid='romeo@montaigu.lit'
              name='My Romeo'>
        </item>
    </query>
</iq>
Example 7. server forwards stanza to managing entity
<iq from='capulet.lit'
    to='pubsub.capulet.lit'
    id='delegate1'
    type='set'>
    <delegation xmlns='urn:xmpp:delegation:2'>
        <forwarded xmlns='urn:xmpp:forward:0'>
            <iq from='juliet@capulet.lit/balcony'
                      id='roster1'
                      type='set'
                      xmlns='jabber:client'>
                <query xmlns='jabber:iq:roster'>
                    <item jid='romeo@montaigu.lit'
                          name='My Romeo'>
                    </item>
                </query>
            </iq>
        </forwarded>
    </delegation>
</iq>

filter.capulet.lit accepts to add Romeo, but all JIDs with a montaigu.lit must be in a "Rivals" group, so it first returns a success result (Romeo is accepted).

Example 8. filtering component accept Romeo
<iq from='pubsub.capulet.lit'
    to='capulet.lit'
    id='delegate1'
    type='result'>
    <delegation xmlns='urn:xmpp:delegation:2'>
        <forwarded xmlns='urn:xmpp:forward:0'>
            <iq to='juliet@capulet.lit/balcony'
                id='roster1'
                type='result'
                xmlns='jabber:client' />
        </forwarded>
    </delegation>
</iq>
Example 9. server decapsulate and send the result with the initial id
<iq to='juliet@capulet.lit/balcony'
    id='roster1'
    type='result' />

At this stade, the entity is accepted, but not added to the roster. filter.capulet.lit is also a privileged entity which can manage "jabber:iq:roster", so it uses this ability to add Romeo in the enforced group:

Example 10. filter.capulet.lit uses privileged entity to add Romeo
<iq to='juliet@capulet.lit'
    from='filter.capulet.lit'
    id='roster2'
    type='set'>
    <query xmlns='jabber:iq:roster'>
        <item jid='romeo@montaigu.lit'
              name='My Romeo'>
            <group>Rivals</group>
        </item>
    </query>
</iq>

The namespace is delegated, but as the stanza is from the managing entity, the server manages it normally. The entity is also privileged, so it can change the stanza of Juliet, the server accepts:

Example 11. server accept new entity in roster
<iq to='filter.capulet.lit'
    from='juliet@capulet.lit'
    id='roster2'
    type='result'/>

The server will then send the roster pushes (with the enforced group) normally.

5. Client Mode Use Cases

5.1 Client Delegation Request Use Case

In client mode, the managing entity is not certified by the server administrator, so the delegation MUST be explicitly allowed by the managed entity. This is initiated by the managing entity (it can be after an interaction with a managed entity, like a subscription).

To request delegation for a particular entity, the managing entity MUST have an <iq/> stanza with 'urn:xmpp:delegation:2' namespace. The <query/> element MUST have a 'to' attribute which specify the entity it wants to manage.

Namespace delegations are asked with a <delegate/> element, which MUST contain a 'namespace' attribute set to the requested namespace.

If an entity want to manage PEP service for Juliet, it can ask the delegation like this:

Example 12. managing entity asks for namespace delegation for one particular entity
<iq from='pubsub.montaigu.lit' to='capulet.lit' type='get' id='delegation1'>
    <query xmlns='urn:xmpp:delegation:2'
           to='juliet@capulet.lit'>
        <delegate namespace='http://jabber.org/protocol/pubsub'/>
    </query>
</iq>

Once received the delegation request, the server ask to the client if it grants access to the requested namespace using Data Forms (XEP-0004) [5]. The server use a challenge which it MUST have generated itself.

Example 13. server asks user for the namespace delegation
<message from='capulet.lit' to='juliet@capulet.lit/balcony'>
    <body>
        pubsub.montaigu.lit wants to manage a feature normally managed by the server.
        Do you allow it to manage the following features?

        Be careful! According management to an entity is a serious thing,
        think twice that you can trust the entity before doing this.
    </body>
    <x xmlns='jabber:x:data' type='form'>
        <title>Delegation request</title>
        <instructions>pubsub.montaigu.lit wants to manage the following features:
            Do you allow it?</instructions>
        <field type='hidden' var='challenge'><value>5439123</value></field>
        <field type='hidden' var='FORM_TYPE'>
            <value>urn:xmpp:delegation:2</value>
        </field>
        <field type='list-single'
            label='Manage PubSub (http://jabber.org/protocol/pubsub)'
            var='http://jabber.org/protocol/pubsub'>
            <value>0</value>
            <option label='No'><value>0</value></option>
            <option label='Yes'><value>1</value></option>
        </field>
    </x>
</message>

The server SHOULD include a warning message, SHOULD translate the namespace to human friendly names (and MAY keep the original namespace in addition) and MUST set the default value to '0' (permission refused). The server MUST use namespaces as field var, so a client can use them to have a customized display.

The client can then answer to the form:

Example 14. client answer to the form
<message from='juliet@capulet.lit/balcony' to='capulet.lit'>
  <x xmlns='jabber:x:data' type='submit'>
    <field var='FORM_TYPE'>
      <value></value>
    </field>
    <field var='challenge'><value>5439123</value></field>
    <field var='http://jabber.org/protocol/pubsub'><value>1</value></field>
  </x>
</message>

Here Juliet allows pubsub.montaigu.lit to manage the PubSub (and then PEP) service.

Finaly, the server notifies the entity of the granted delegation. It do this in the same way as for admin mode, except that the <delegation/> element has an attitional 'to' attribute set to the managed entity bare jid:

Example 15. server advertise delegated namespaces for juliet
<message from='capulet.net' to='pubub.capulet.lit' id='6789'>
    <delegation xmlns='urn:xmpp:delegation:2' to='juliet@capulet.lit'>
        <delegated namespace='http://jabber.org/protocol/pubsub'/>
    </delegation>
</message>

5.2 Server Forward Stanza

The managing entity can now manage the namespace in a similar way as in admin mode but with different rules:

  1. if the stanza is directed to the delegating server (no 'to' attribute, or 'to' attribute with the server own JID), and the 'from' attribute belong to a managed entity (e.g. juliet@capulet.lit/balcony if juliet@capulet.lit is a managed entity) and the namespace of the stanza has been delegated by the managed entity, then the delegating server MUST forward it to the managing entity accepted by the managed entity, in the same way as in admin mode.
  2. if the stanza is directed to the bare jid (and only the bare jid) of the managed entity (e.g. the 'to' attribute is set to juliet@capulet.lit and the namespace has been delegated by the managed entity, then the server MUST forward it to the managing entity accepted by the managed entity, in the same way as in admin mode, for any 'from' attribute but the jid of the managing entity.
  3. in all other cases, the server MUST NOT forward the stanza

6. Configuration

Server SHOULD provide a way for clients to check already delegated namespaces, and revoke them by using Ad-Hoc Commands (XEP-0050) [6] on the well-defined command node 'urn:xmpp:delegation:2#configure'.

If present, the configuration commands MUST allow at least to check delegations granted to a managing entity, and to revoke them. A server MAY offer an option to keep delegations from one session to an other (see business rules).

7. Discovering Support

7.1 Announce

If a server or an entity supports the namespace delegation protocol, it MUST report that fact by including a service discovery feature of "urn:xmpp:delegation:2" in response to a Service Discovery (XEP-0030) [7] information request:

Example 16. service discovery information request
<iq from='pubsub.capulet.lit'
    id='disco1'
    to='capulet.lit'
    type='get'>
  <query xmlns='http://jabber.org/protocol/disco#info'/>
</iq>
Example 17. service discovery information response
<iq from='capulet.lit'
    id='disco1'
    to='pubsub.capulet.lit'
    type='result'>
  <query xmlns='http://jabber.org/protocol/disco#info'>
    ...
    <feature var='urn:xmpp:delegation:2'/>
    ...
  </query>
</iq>

7.2 Nesting

7.2.1 General Case

When a server delegates a namespace to a managing entity, the later can have particular features which must be advertised by the former with disco protocol.

This is done by using a disco node, which is built in the following way: if pubsub.capulet.int manages pubsub namespace, it MUST report that fact in discovery feature, and have a 'urn:xmpp:delegation:2::http://jabber.org/protocol/pubsub' node which reports the managed features.

The node name is obtained by concatenating this XEP namespace (urn:xmpp:delegation:2), a '::' separator, and the delegated namespace (here http://jabber.org/protocol/pubsub).
The server MUST advertise the result in its own discovery answer, and MUST ignore features of its internal component (here internal PubSub service).

In the following example, the capulet.int server delegates its internal PEP component to pubsub.capulet.int. capulet.int only supports REQUIRED PubSub features and auto-create, while pubsub.capulet.int supports REQUIRED PubSub features and publish-options, but not auto-create.
juliet@capulet.int asks its server what it is capable of, she is specially interested in PubSub capabilities.

Example 18. Juliet asks her server its available features
<iq from='juliet@capulet.lit/balcony'
    id='disco1'
    to='capulet.lit'
    type='get'>
  <query xmlns='http://jabber.org/protocol/disco#info'/>
</iq>

Server delegates its PubSub namespace to pubsub.capulet.lit, so it asks its available features for this namespace like this:

Example 19. capulet.lit requests disco infos for pubsub namespace to pubsub.capulet.lit
<iq from='capulet.lit'
    id='disco2'
    to='pubsub.capulet.lit'
    type='get'>
  <query xmlns='http://jabber.org/protocol/disco#info'
         node='urn:xmpp:delegation:2::http://jabber.org/protocol/pubsub'/>
</iq>

Note that in real situation, server has probably this information already in cache (see Implementation Notes).
pubsub.capulet.lit returns its available features:

Example 20. pubsub.capulet.lit returns features to nest
<iq from='pubsub.capulet.lit'
    id='disco2'
    to='capulet.lit'
    type='result'>
  <query xmlns='http://jabber.org/protocol/disco#info'
         node='urn:xmpp:delegation:2::http://jabber.org/protocol/pubsub'>
        <feature var='http://jabber.org/protocol/pubsub'/>
        <feature var='http://jabber.org/protocol/pubsub#publish'/>
        <feature var='http://jabber.org/protocol/pubsub#subscribe'/>
        <feature var='http://jabber.org/protocol/pubsub#publish-options'/>
  </query>
</iq>

Server include the results in its own discovery info results:

Example 21. capulet.lit return disco info including features from pubsub.capulet.lit
<iq from='capulet.lit'
    id='disco1'
    to='juliet@capulet.lit/balcony'
    type='result'>
  <query xmlns='http://jabber.org/protocol/disco#info'>
        <feature var='urn:xmpp:delegation:2'/>
        ...
        <feature var='http://jabber.org/protocol/pubsub'/>
        <feature var='http://jabber.org/protocol/pubsub#publish'/>
        <feature var='http://jabber.org/protocol/pubsub#subscribe'/>
        <feature var='http://jabber.org/protocol/pubsub#publish-options'/>
        ...
  </query>
</iq>

Note that 'http://jabber.org/protocol/pubsub#auto-create' is not available.

N.B.: In the special case of attribute filtering, the server still display managing entity's features for the whole delegated namespace instead of its own internal ones.

7.2.2 Nesting of Bare JID Disco Info

As an entity may ask for discovery information on bare JID, which the server would answer, the managing entity must be able to send this kind of information.

To do so, the mechanism is the same as for server features, but the separator is ':bare:' instead of '::':

Example 22. Juliet Asks Features for Her Own Bare JID
<iq from='juliet@capulet.lit/balcony'
    id='disco3'
    to='juliet@capulet.lit'
    type='get'>
  <query xmlns='http://jabber.org/protocol/disco#info'/>
</iq>

Server delegate its PubSub namespace to pubsub.capulet.lit, so it ask its available features for this namespace like this:

Example 23. capulet.lit requests disco infos for pubsub namespace to pubsub.capulet.lit
<iq from='capulet.lit'
    id='disco4'
    to='pubsub.capulet.lit'
    type='get'>
  <query xmlns='http://jabber.org/protocol/disco#info'
         node='urn:xmpp:delegation:2:bare:http://jabber.org/protocol/pubsub'/>
</iq>

As for general case, server has probably this information already in cache.
pubsub.capulet.lit returns its available features:

Example 24. pubsub.capulet.lit returns features to nest
<iq from='pubsub.capulet.lit'
    id='disco4'
    to='capulet.lit'
    type='result'>
    <query xmlns='http://jabber.org/protocol/disco#info'
           node='urn:xmpp:delegation:2:bare:http://jabber.org/protocol/pubsub'>
        <identity category='pubsub' type='pep'/>
        <feature var='http://jabber.org/protocol/pubsub#access-presence'/>
        <feature var='http://jabber.org/protocol/pubsub#auto-create'/>
        <feature var='http://jabber.org/protocol/pubsub#auto-subscribe'/>
        <feature var='http://jabber.org/protocol/pubsub#config-node'/>
        <feature var='http://jabber.org/protocol/pubsub#create-and-configure'/>
        <feature var='http://jabber.org/protocol/pubsub#create-nodes'/>
        <feature var='http://jabber.org/protocol/pubsub#filtered-notifications'/>
        <feature var='http://jabber.org/protocol/pubsub#persistent-items'/>
        <feature var='http://jabber.org/protocol/pubsub#publish'/>
        <feature var='http://jabber.org/protocol/pubsub#retrieve-items'/>
        <feature var='http://jabber.org/protocol/pubsub#subscribe'/>
        ...
    </query>
</iq>

Then the server returns the answer to Juliet, as in general case, with requested bare JID in 'from' field.

Example 25. capulet.lit returns disco info to Juliet
<iq from='juliet@capulet.lit'
    id='disco3'
    to='juliet@capulet.lit/balcony'
    type='result'>
    <query xmlns='http://jabber.org/protocol/disco#info'>
        <identity category='account' type='registered'/>
        <identity category='pubsub' type='pep'/>
        <feature var='http://jabber.org/protocol/pubsub#access-presence'/>
        <feature var='http://jabber.org/protocol/pubsub#auto-create'/>
        <feature var='http://jabber.org/protocol/pubsub#auto-subscribe'/>
        <feature var='http://jabber.org/protocol/pubsub#config-node'/>
        <feature var='http://jabber.org/protocol/pubsub#create-and-configure'/>
        <feature var='http://jabber.org/protocol/pubsub#create-nodes'/>
        <feature var='http://jabber.org/protocol/pubsub#filtered-notifications'/>
        <feature var='http://jabber.org/protocol/pubsub#persistent-items'/>
        <feature var='http://jabber.org/protocol/pubsub#publish'/>
        <feature var='http://jabber.org/protocol/pubsub#retrieve-items'/>
        <feature var='http://jabber.org/protocol/pubsub#subscribe'/>
        ...
    </query>
</iq>

7.2.3 Service Discovery Extensions

Extensions of Service Discovery as specified in Service Discovery Extensions (XEP-0128) [8] follow the same rules: for the delegated namespace, internal extensions MUST be removed and extensions of managing entity MUST be included instead.

7.2.4 Remaining Discovery Infos

It may be necessary for a managing entity to advertise feature on a node which is unknown at the time of configuration. This is notably the case for a PEP component: features must be advertisable on disco nodes mapping pubsub nodes.

To allows that, the special namespace 'urn:xmpp:delegation:2:bare:disco#info:*' is used, and means "delegate information discovery requests made on bare jids for any discovery node which is not already managed by the server".

Example 26. Juliet Asks Features for the Microblog Node 'urn:xmpp:microblog:0' for her Own Bare JID
<iq from='juliet@capulet.lit/balcony'
    id='disco1'
    to='juliet@capulet.lit'
    type='get'>
    <query xmlns='http://jabber.org/protocol/disco#info' node='urn:xmpp:microblog:0'/>
</iq>

The node 'urn:xmpp:microblog:0' is not managed by the server. Normally, this would result as an <item-not-found> <iq/> error, but the namespace 'urn:xmpp:delegation:2:bare:disco#info:*' is delegated to pubsub.capulet.lit, thus the server delegate the stanza to the managing entity:

Example 27. Server Delegates Disco Request to pubsub.capulet.lit
<iq from='capulet.lit'
    to='pubsub.capulet.lit'
    id='delegate_disco_1'
    type='set'>
    <delegation xmlns='urn:xmpp:delegation:2'>
        <forwarded xmlns='urn:xmpp:forward:0'>
            <iq from='juliet@capulet.lit/balcony'
                id='disco1'
                to='juliet@capulet.lit'
                type='get'>
                <query xmlns='http://jabber.org/protocol/disco#info' node='urn:xmpp:microblog:0'/>
            </iq>
        </forwarded>
    </delegation>
</iq>

The managing entity answers with its own disco features for the requested node:

Example 28. pubsub.capulet.lit Replies With its Disco Infos for this Node
<iq from='pubsub.capulet.lit'
    to='capulet.lit'
    id='delegate_disco_1'
    type='result'>
    <delegation xmlns='urn:xmpp:delegation:2'>
        <forwarded xmlns='urn:xmpp:forward:0'>
            <iq to='juliet@capulet.lit/balcony'
                id='disco1'
                type='result'
                xmlns='jabber:client'>
                <query xmlns="http://jabber.org/protocol/disco#info" node="urn:xmpp:microblog:0">
                    <identity type="leaf" category="pubsub"/>
                    <x xmlns="jabber:x:data" type="result">
                        <field var="FORM_TYPE" type="hidden">
                            <value>http://jabber.org/protocol/pubsub#meta-data</value>
                        </field>
                        <field var="pubsub#node_type" type="text-single">
                            <value>leaf</value>
                        </field>
                        <field var="pubsub#persist_items" type="boolean">
                            <value>true</value>
                        </field>
                        <field var="pubsub#max_items" type="text-single">
                            <value>max</value>
                        </field>
                        <field var="pubsub#access_model" type="list-single">
                            <value>whitelist</value>
                        </field>
                    </x>
                    <feature var="http://jabber.org/protocol/rsm"/>
                    <feature var="http://jabber.org/protocol/pubsub#rsm"/>
                    <feature var="urn:xmpp:order-by:1"/>
                </query>
            </iq>
        </forwarded>
    </delegation>
</iq>

Then the server decapsulate the <iq/> result, validate it as explained in Server Forwards Delegated <iq/> Stanza, and send the result to Juliet:

Example 29. capulet.lit Sends the Disco Infos to Juliet
<iq to='juliet@capulet.lit/balcony'
    id='disco1'
    type='result'
    xmlns='jabber:client'>
    <query xmlns="http://jabber.org/protocol/disco#info" node="urn:xmpp:microblog:0">
        <identity type="leaf" category="pubsub"/>
        <x xmlns="jabber:x:data" type="result">
            <field var="FORM_TYPE" type="hidden">
                <value>http://jabber.org/protocol/pubsub#meta-data</value>
            </field>
            <field var="pubsub#node_type" type="text-single">
                <value>leaf</value>
            </field>
            <field var="pubsub#persist_items" type="boolean">
                <value>true</value>
            </field>
            <field var="pubsub#max_items" type="text-single">
                <value>max</value>
            </field>
            <field var="pubsub#access_model" type="list-single">
                <value>whitelist</value>
            </field>
        </x>
        <feature var="http://jabber.org/protocol/rsm"/>
        <feature var="http://jabber.org/protocol/pubsub#rsm"/>
        <feature var="urn:xmpp:order-by:1"/>
    </query>
</iq>

7.2.5 Bare JID Disco Items

A managing entity must be able to answer items discovery requests on bare jids. For PEP components, this is used to show available nodes on the service. Furthermore, An information discovery request or an items discovery requests on a node corresponding to an item advertised by the managing entity must be forwarded to the managing entity too.

This is done by using the special namespace 'urn:xmpp:delegation:2:bare:disco#items:*' which means "delegate items discovery made on bare jids with no node specified and all items discovery requests made on bare jids with a node which is not already managed by the server".

Note: When no node is used, and unlike the disco#info case, the server SHOULD NOT nest its internal items with the ones from managing entity. The reason is that bare jids disco items are usually used for PEP nodes, and the server would then mix internal PEP nodes with the managing entity nodes, which would be confusing for XMPP clients and end-users. The server implementation MAY choose to nest items anyway, in which case the mechanism is the same as for disco#info.

A server SHOULD NOT cache result of forwarded disco#items requests, as this is highly dynamic.

Example 30. Juliet Discover Items from her Own Bare JID
<iq from='juliet@capulet.lit/balcony'
    id='disco_items_1'
    to='juliet@capulet.lit'
    type='get'>
    <query xmlns='http://jabber.org/protocol/disco#items'/>
</iq>

The namespace 'urn:xmpp:delegation:2:bare:disco#items:*' is delegated to pubsub.capulet.lit, thus the server delegate the stanza to the managing entity:

Example 31. Server Delegates Disco Items Request to pubsub.capulet.lit
<iq from='capulet.lit'
    to='pubsub.capulet.lit'
    id='delegate_disco_items_1'
    type='set'>
    <delegation xmlns='urn:xmpp:delegation:2'>
        <forwarded xmlns='urn:xmpp:forward:0'>
            <iq from='juliet@capulet.lit/balcony'
                id='disco_items_1'
                to='juliet@capulet.lit'
                type='get'>
                <query xmlns='http://jabber.org/protocol/disco#items'/>
            </iq>
        </forwarded>
    </delegation>
</iq>

The managing entity answers with its own disco items for Juliet's JID:

Example 32. pubsub.capulet.lit Replies With its Disco Items for this JID
<iq from='pubsub.capulet.lit'
    to='capulet.lit'
    id='delegate_disco_items_1'
    type='result'>
    <delegation xmlns='urn:xmpp:delegation:2'>
        <forwarded xmlns='urn:xmpp:forward:0'>
            <iq to='juliet@capulet.lit/balcony'
                id='disco_items_1'
                type='result'
                xmlns='jabber:client'>
                <query xmlns="http://jabber.org/protocol/disco#items">
                    <item jid="juliet@capulet.int" node="http://jabber.org/protocol/mood"/>
                    <item jid="juliet@capulet.int" node="http://jabber.org/protocol/activity"/>
                        …
                    <item jid="juliet@capulet.int" node="urn:xmpp:microblog:0"/>
                        …
                </query>
            </iq>
        </forwarded>
    </delegation>
</iq>

Then the server decapsulate the <iq/> result, validate it as explained in Server Forwards Delegated <iq/> Stanza, and send the result to Juliet:

Example 33. capulet.lit Sends the Disco Items to Juliet
<iq to='juliet@capulet.lit/balcony'
    id='disco_items_1'
    type='result'
    xmlns='jabber:client'>
    <query xmlns="http://jabber.org/protocol/disco#items">
        <item jid="juliet@capulet.int" node="http://jabber.org/protocol/mood"/>
        <item jid="juliet@capulet.int" node="http://jabber.org/protocol/activity"/>
            …
        <item jid="juliet@capulet.int" node="urn:xmpp:microblog:0"/>
            …
    </query>
</iq>

Juliet now wants to know the IDs of blog items which has been published on her blog, to do so she does an items discovery request on her own bare jid with the 'urn:xmpp:microblog:0' node:

Example 34. Juliet Discovers Items for the Microblog Node 'urn:xmpp:microblog:0' on her Own Bare JID
<iq from='juliet@capulet.lit/balcony'
    id='disco_items_2'
    to='juliet@capulet.lit'
    type='get'>
    <query xmlns='http://jabber.org/protocol/disco#items' node='urn:xmpp:microblog:0'/>
</iq>

Because the special namespace 'urn:xmpp:delegation:2:bare:disco#items:*' is delegated to pubsub.capulet.lit, the server forward the request to this managing entity:

Example 35. Server Delegates Disco Items Request to pubsub.capulet.lit
<iq from='capulet.lit'
    to='pubsub.capulet.lit'
    id='delegate_disco_2'
    type='set'>
    <delegation xmlns='urn:xmpp:delegation:2'>
        <forwarded xmlns='urn:xmpp:forward:0'>
            <iq from='juliet@capulet.lit/balcony'
                id='disco_items_2'
                to='juliet@capulet.lit'
                type='get'>
                <query xmlns='http://jabber.org/protocol/disco#items' node='urn:xmpp:microblog:0'/>
            </iq>
        </forwarded>
    </delegation>
</iq>

The managing entity answers with its own disco items for the requested entity and node (pubsub.capulet.lit being a PEP service, the items are actually Juliet's blog items IDs):

Example 36. pubsub.capulet.lit Replies With its Disco Items for this Entity and Node
<iq from='pubsub.capulet.lit'
    to='capulet.lit'
    id='delegate_disco_2'
    type='result'>
    <delegation xmlns='urn:xmpp:delegation:2'>
        <forwarded xmlns='urn:xmpp:forward:0'>
            <iq to='juliet@capulet.lit/balcony'
                id='disco_items_2'
                type='result'
                xmlns='jabber:client'>
                <query xmlns="http://jabber.org/protocol/disco#items" node="urn:xmpp:microblog:0">
                    <item name="o-romeo-romeo-wherefore-art-thou-romeo-G1aF" jid="juliet@capulet.lit"/>
                    <item name="thou-know-st-the-mask-of-night-is-on-my-face-2avF" jid="juliet@capulet.lit"/>
                    <item name="balcony-and-privacy-afFG" jid="juliet@capulet.lit"/>
                </query>
            </iq>
        </forwarded>
    </delegation>
</iq>

The server decapsulates the <iq/> result, validate it as explained in Server Forwards Delegated <iq/> Stanza, and send the result to Juliet:

Example 37. capulet.lit Sends the Disco Items to Juliet
<iq to='juliet@capulet.lit/balcony'
    id='disco_items_2'
    type='result'
    xmlns='jabber:client'>
    <query xmlns="http://jabber.org/protocol/disco#items" node="urn:xmpp:microblog:0">
        <item name="o-romeo-romeo-wherefore-art-thou-romeo-G1aF" jid="juliet@capulet.lit"/>
        <item name="thou-know-st-the-mask-of-night-is-on-my-face-2avF" jid="juliet@capulet.lit"/>
        <item name="balcony-and-privacy-afFG" jid="juliet@capulet.lit"/>
    </query>
</iq>

8. Business Rules

  1. In client mode, server MAY keep delegations granted to an entity by a client from one session to an other, but if it does so, it MUST provide configuration like explained in the suitable section. If server offers this feature, it SHOULD add a field directly in configuration commands.
  2. If a client can't check or revoke delegations (i.e. it doesn't support Ad-Hoc Commands (XEP-0050) [6]) when granting them, the server MUST NOT keep granted delegations from one session to an other, and delegations will be asked on each new session.
  3. If delegations are changed during a session, server MUST notify managing entity of the new delegations, like in client delegation request use case.
  4. If delegations are kept between sessions in client mode, and the managing entity is not available or return an error, the server MUST return an <iq/> error with condition <service-unavailable/> when a delegated namespace is requested, like explained in "Server Forwards Delegated <iq/> Stanza" section.
  5. The namespace of this XEP (urn:xmpp:delegation:2) MUST NOT be delegated. If an entity requests it, the server MUST return a <forbidden/> error.

9. Implementation Notes

  1. As admin mode is far more easy to implement than client mode, and client mode may impact performances, a server MAY choose to only implement the former.
  2. Because of the performance impact, a server SHOULD ask for disco features to nest to managing entity when delegation is accepted, and keep them in cache.
  3. RFC 6120 [9] section 10.1 require in-order processing of stanzas, which may be problematic for this extension: either the server blocks the traffic until the managing entity answers - which can lead to severe performance impact -, or the server doesn't block and may loose order. The recommended way is to not block the traffic while waiting for managing entity answer to avoid performance issues. A future version of this XEP may include an attribute to request traffic blocking. In admin mode the server implementation MAY chooses to have a blocking option (which SHOULD be per namespace, not global).

10. Security Considerations

  1. Managing entity can manage sensitive data, admin delegation should be granted carefuly, only if you absolutely trust the entity.
  2. A server MAY choose to filter allowed namespaces. In this case, it MUST always set the allowed type of filtered namespaces to 0.
  3. In case of filtering, an allowlist system is more secure and SHOULD be prefered to a blocklist (idealy, configuration would allow no filtering, allowlist filtering and blocklist filtering).
  4. Managing entity must be careful about not leaking the existence of an account (see XEP-0030 Security Considerations).

11. IANA Considerations

This document requires no interaction with the Internet Assigned Numbers Authority (IANA) [10].

12. XMPP Registrar Considerations

12.1 Protocol Namespaces

The XMPP Registrar [11] includes 'urn:xmpp:delegation:2' in its registry of protocol namespaces (see <https://xmpp.org/registrar/namespaces.html>).

12.2 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.

13. XML Schema

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

<xs:schema
    xmlns:xs='http://www.w3.org/2001/XMLSchema'
    targetNamespace='urn:xmpp:delegation:2'
    xmlns='urn:xmpp:delegation:2'
    elementFormDefault='qualified'>

  <xs:import namespace='urn:xmpp:forward:0'
      schemaLocation='http://xmpp.org/schemas/forward.xsd'/>

  <xs:element name='query'>
      <xs:complexType>
          <xs:attribute name='to' use='required' type='xs:string'/>
          </xs:attribute>
          <xs:element name='delegate'
                      maxOccurs='unbounded'>
              <xs:complexType>
                  <xs:attribute name='namespace' use='required' type='xs:string'/>
              </xs:complexType>
          </xs:element>
      </xs:complexType>
  </xs:element>

  <xs:element name='delegation'>
      <xs:complexType>
          <xs:element ref='urn:xmpp:forward:0' minOccurs='0' maxOccurs='1' />
          <xs:element name='delegated'
                      minOccurs='0'
                      maxOccurs='unbounded'>
              <xs:complexType>
                  <xs:attribute name='namespace' use='required' type='xs:string'/>
                  <xs:element name='attribute'
                              minOccurs='0'
                              maxOccurs='unbounded'>
                      <xs:complexType>
                          <xs:attribute name='name' use='required' type='xs:string'/>
                      </xs:complexType>
                  </xs:element>
              </xs:complexType>
          </xs:element>
      </xs:complexType>
  </xs:element>

</xs:schema>

14. Acknowledgements

This XEP is linked with Privileged Entity (XEP-0356) [3] and works in a similar way.

The client mode delegation mechanism is inspired from Remote Roster Management (XEP-0321) [12] permission request.

Thanks to Adrien Cossa for his typos/style corrections

Thanks to Philipp Hancke, Dave Cridland, Kurt Zeilenga, Sergey Dobrov and Анна Мухаррам for their feedbacks.

Appendices

Appendix A: Document Information

Series
XEP
Number
0355
Publisher
XMPP Standards Foundation
Status
Experimental
Type
Standards Track
Version
0.5
Last Updated
2021-10-15
Approving Body
XMPP Council
Dependencies
XMPP Core, XEP-0004, XEP-0297
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

Copyright

This XMPP Extension Protocol is copyright © 1999 – 2020 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).

Visual Presentation

The HTML representation (you are looking at) is maintained by the XSF. It is based on the YAML CSS Framework, which is licensed under the terms of the CC-BY-SA 2.0 license.

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

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

3. XEP-0356: Privileged Entity <https://xmpp.org/extensions/xep-0356.html>.

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

5. XEP-0004: Data Forms <https://xmpp.org/extensions/xep-0004.html>.

6. XEP-0050: Ad-Hoc Commands <https://xmpp.org/extensions/xep-0050.html>.

7. XEP-0030: Service Discovery <https://xmpp.org/extensions/xep-0030.html>.

8. XEP-0128: Service Discovery Extensions <https://xmpp.org/extensions/xep-0128.html>.

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

10. 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/>.

11. 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/>.

12. XEP-0321: Remote Roster Management <https://xmpp.org/extensions/xep-0321.html>.

Appendix H: Revision History

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

  1. Version 0.5 (2021-10-15)
    jp
  2. Version 0.4.2 (2021-03-04)

    Cross-document editorial adjustments for inclusive language.

    mw
  3. Version 0.4.1 (2018-11-03)
    Fix a bunch of typos, batch-style.
    pep
  4. Version 0.4 (2017-09-11)
    Defer due to lack of activity.
    XEP Editor (jwi)
  5. Version 0.3 (2016-08-01)
    jp
  6. Version 0.2.1 (2015-10-15)

    Corrected examples (Stefan Strigler).

    XEP Editor (mam)
  7. Version 0.2 (2014-03-21)

    Several updates according to feedbacks:

    jp
  8. Version 0.1 (2014-12-18)

    Initial published version approved by the XMPP Council.

    XEP Editor (mam)
  9. Version 0.0.1 (2014-11-13)

    First draft.

    jp

Appendix I: Bib(La)TeX Entry

@report{poisson2014xep0355,
  title = {Namespace Delegation},
  author = {Poisson, Jérôme},
  type = {XEP},
  number = {0355},
  version = {0.5},
  institution = {XMPP Standards Foundation},
  url = {https://xmpp.org/extensions/xep-0355.html},
  date = {2014-11-13/2021-10-15},
}

END