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.
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.
Roster access is granted in the server configuration. Roster access can have 4 types:
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
<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
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:
<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:
<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>
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:
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.
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':
<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>
Now that pubsub.capulet.lit is allowed, it can send messages using <forwarded/> elements.
<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:
<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>
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.
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"
Once the "presence" permission is granted, the server send presence informations:
<presence from='juliet@capulet.lit/balcony'
id='presence1'
xml:lang='en'>
<show>chat</show>
<status>Staying on the balcony</status>
</presence>
<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>
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).
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"
<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.
<presence from='romeo@montaigu.lit/orchard'/>
<presence from='romeo@montaigu.lit/orchard'
to='juliet@capulet.lit'/>
<presence from='romeo@montaigu.lit/orchard'
to='pubsub.capulet.lit'/>
This document requires no interaction with the Internet Assigned Numbers Authority (IANA) [7].
The XMPP Registrar [8] includes 'urn:xmpp:privilege:1' in its registry of protocol namespaces (see <https://xmpp.org/registrar/namespaces.html>).
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.
<?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>
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.
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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.
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>.
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".
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/>.
Note: Older versions of this specification might be available at http://xmpp.org/extensions/attic/
Several updates according to feedbacks + review:
Initial published version approved by the XMPP Council.
First draft.
END