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<xep>
<header>
  <title>Attribute Based Access Control</title>
  <abstract>This specification adapt Attribute Based Access Control (ABAC) model to XMPP</abstract>
  <legal>
    <copyright>This XMPP Extension Protocol is copyright (c) 1999 - 2014 by the XMPP Standards Foundation (XSF).</copyright>
    <permissions>Permission is hereby granted, free of charge, to any person obtaining a copy of this specification (the &quot;Specification&quot;), 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.</permissions>
    <warranty>## NOTE WELL: This Specification is provided on an &quot;AS IS&quot; 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. In no event shall the XMPP Standards Foundation or the authors of this Specification be liable for any claim, damages, or other liability, whether in an action of contract, tort, or otherwise, arising from, out of, or in connection with the Specification or the implementation, deployment, or other use of the Specification. ##</warranty>
    <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 out of the use or inability to use 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.</liability>
    <conformance>This XMPP Extension Protocol has been contributed in full conformance with the XSF's Intellectual Property Rights Policy (a copy of which may be found at &lt;<link url='http://xmpp.org/extensions/ipr-policy.shtml'>http://xmpp.org/extensions/ipr-policy.shtml</link>&gt; or obtained by writing to XSF, P.O. Box 1641, Denver, CO 80201 USA).</conformance>
  </legal>
  <number>xxxx</number>
  <status>ProtoXEP</status>
  <type>Standards Track</type>
  <sig>Standards</sig>
  <approver>Council</approver>
  <dependencies>
    <spec>XMPP Core</spec>
    <spec>XEP-0114</spec>
    <spec>XEP-0004</spec>
  </dependencies>
  <supersedes/>
  <supersededby/>
  <shortname>NOT_YET_ASSIGNED</shortname>
  <author>
    <firstname>Jérôme</firstname>
    <surname>Poisson</surname>
    <email>goffi@goffi.org</email>
    <jid>goffi@jabber.fr</jid>
  </author>
  <revision>
    <version>0.0.1</version>
    <date>2014-05-09</date>
    <initials>jp</initials>
    <remark><p>First draft.</p></remark>
  </revision>
</header>

<section1 topic='Introduction' anchor='intro'>
    <p>Different access control models are used in XMPP, most of time Role Based Access Model (RBAC) like in MUC, or Identity Based Access Model (IBAC) like [...]</p>
    <p>Privileged entities have numerous advantages, including:</p>
        <ul>
            <li>a step forward in decentralization: it is possible for an entity to do tasks which were before reserved to server itself. For example, a privileged pubsub component can offer access model based on publisher's roster</li>
            <li>better integration of components: a gateway can add items to an entity roster itself</li>
            <li>possibility to overpass a server limitation (typically: incomplete PEP implementation)</li>
            <li>quick development cycle: developers can implement the components they need without waiting for a new server release</li>
            <li>server agnostic</li>
        </ul>
        <p>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 <link url='#acks'>Acknowledgements section</link> for more details</p>
</section1>

<section1 topic='Requirements' anchor='reqs'>
    <p>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):</p>
        <ul>
            <li>get and modify the roster of any entity managed by the server</li>
            <li>send a &MESSAGE; stanza on behalf of the server</li>
            <li>access &PRESENCE; informations for entities in a managed entity's roster (and for managed entity itself)</li>
        </ul>
    <p>The privilege mechanism MUST be totally transparent for the managed entities.</p>
</section1>

<section1 topic='Glossary' anchor='glossary'>
  <ul>
    <li><strong>Privileged entity</strong> — the entity which has a privileged status.</li>
    <li><strong>Managed entity</strong> — the entity that is managed by a privileged entity.</li>
  </ul>
</section1>

<section1 topic='Accessing roster' anchor='access_roster'>

    <section2 topic='Server Allows Roster Access' anchor='server_roster'>
        <p>Roster access is granted in the server configuration. Roster access can have 4 types:</p> 
            <ul>
                <li><strong>none</strong> — the entity is not allowed to access managed entity roster at all. This MUST be the default value.</li>
                <li><strong>get</strong> — the entity is allowed to send &IQ; stanzas of type <em>'get'</em> for the namespace 'jabber:iq:roster'.</li>
                <li><strong>set</strong> — the entity is allowed to send &IQ; stanzas of type <em>'set'</em> for namespace 'jabber:iq:roster'.</li>
                <li><strong>both</strong> — the entity is allowed to send &IQ; stanzas of type <em>'get'</em> and <em>'set'</em> for namespace 'jabber:iq:roster'.</li>
            </ul>
    </section2>

    <section2 topic='Server Advertise Entity Of Allowed Permission' anchor='advertise_roster'>
        <p>Once an entity is authenticated and stream is started, the server send it a &MESSAGE; stanza with a &lt;privilege&gt; elements which MUST have the namespace 'urn:xmpp:privilege:0'. This element contains &lt;perm&gt; elements which MUST contain a 'namespace' attribute of the value "jabber:iq:roster" and a 'type' attribute which must correspond to the type configured as specified in <link url='#server_roster'>"Server Allows Roster Access" section</link></p>
            <example caption='Server Advertise Roster Privilege'><![CDATA[
<message from='capulet.net' to='pubub.capulet.lit' id='12345'>
    <privilege xmlns='urn:xmpp:privilege:0'>
        <perm namespace='jabber:iq:roster' type='both'/>
    </privilege>
</message>
    ]]></example>
<p>Here <em>pubsub.capulet.lit</em> is allowed to do <em>get</em> and <em>set</em> operations on all entities managed by capulet.lit</p>
    </section2>

    <section2 topic='Privileged Entity Manage Roster' anchor='priv_manage_roster'>
        <p>Doing a <em>get</em> or <em>set</em> operation on the roster of a managed entity is done in the usual way (as described in &rfc6121;  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 <em>get</em> or <em>set</em> the roster of managed entity, and MUST return a &forbidden; error if it is not the case:</p>
            <example caption='Privileged Entity Get Managed Entity Roster'><![CDATA[
<iq id='roster1'
    from='pubsub.capulet.lit'
    to='juliet@example.com'
    type='get'
    id='roster1'>
        <query xmlns='jabber:iq:roster'/>
</iq>
            ]]></example>

        <p>The server then answers normally, as it would have done to the managed entity:</p>
            <example caption='Server Answers To Privileged Entity'><![CDATA[
<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>
            ]]></example>

    </section2>
</section1>

<section1 topic='Message Permission' anchor='message'>
    <section2 topic='Authorizing Messages' anchor='auth_mess'>
        <p>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:</p>
            <ul>
                <li><strong>none</strong> — the entity is not allowed to send &MESSAGE; stanza in the name of the server. This MUST be the default value.</li>
                <li><strong>outgoing</strong> — the entity is allowed to send &MESSAGE; stanzas in the name of the server, according to following restrictions.</li>
            </ul>
        <p>A privileged entity can then send message on the behalf either of the server or of a bare JID of the server, using &xep0297;, with the following restrictions:</p>
        <ol>
            <li>forwarded &MESSAGE; 'type' attribute has the value of "headline"</li>
            <li>forwarded &MESSAGE; 'from' attribute MUST be a bare JID from the server, no resource is allowed</li>
        </ol>
        <p>If any of this rules is violated, the server MUST return a &lt;not-authorized/&gt; stream error and close the connection, as explained in &rfc6120; section 4.9.3.12.</p>
    </section2>

    <section2 topic='Advertising Permission' anchor='advertise_mess'>
        <p>Server advertise "message" permission in the same way as for "roster" permission, except that 'namespace' attribute has the value of "message", and the 'type' attribute as a value of 'outgoing':</p>
        <example caption='Server Advertise Roster And Message Privileges'><![CDATA[
<message from='capulet.net' to='pubub.capulet.lit' id='54321'>
    <privilege xmlns='urn:xmpp:privilege:0'>
        <perm namespace='jabber:iq:roster' type='both'/>
        <perm namespace='message' type='outgoing'/>
    </privilege>
</message>
]]></example>
    </section2>

    <section2 topic='Sending messages' anchor='sending_mess'>
        <p>Now that <em>pubsub.capulet.lit</em> is allowed, it can send messages using &lt;forwarded/&gt; elements.</p>
        <example caption='privileged entity send a notificaction message'><![CDATA[
<message from='pubsub.capulet.lit' to='capulet.lit' id='notif1'>
    <forwarded xmlns='urn:xmpp:forward:0'>
        <message from='juliet@capulet.lit'
            id='foo'
            to='romeo@montague.lit/orchard'
            type='headline'
            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>
</message>
        ]]></example>
        <p>The server sees that forwarded message type is '<em>headline</em>', that <em>juliet@capulet.lit</em> is a bare JID of the server, and that outgoing message permission was granted in admin mode (so all bare JIDs from server are allowed); it can now send the notification:</p>
        <example caption='server sends the notification as if it was originating from him'><![CDATA[
<message from='juliet@capulet.lit'
    id='bar'
    to='romeo@montague.lit/orchard'
    type='headline'>
    <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>
    ]]></example>
    </section2>
</section1>

<section1 topic='Presence Permission' anchor='presence'>
    <section2 topic='Managed Entity Presence' anchor='managed_ent_presence'>
        <p>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.</p>
        <p>This is allowed in server configuration in the same way as for <em>roster</em> and <em>message</em> permissions. The "presence" type can have the following values:</p>
            <ul>
                <li><strong>none</strong> — the entity is not allowed to access &PRESENCE; informations at all. This MUST be the default value.</li>
                <li><strong>managed_entity</strong> — the entity is allowed to receive managed entity presence (see below).</li>
                <li><strong>roster</strong> — the entity is allowed to receive presence informations of managed entity contacts, see <link url='#roster_presence'>Roster Presence section</link>.</li>
            </ul>
        <p>If the privilege is granted, the server MUST use a directed presence, as specified in &rfc6121; section 4.6 on the behalf of managed entity each time its presence information change.</p>
    </section2>

    <section2 topic='Advertising Permission' anchor='advertise_managed_presence'>
        <p>Server advertise "presence" permission in the same way as for "roster" or "message" permissions, except that 'namespace' attribute has the value of "presence", and the 'type' attribute has a value of "managed_entity"</p>
    </section2>

    <section2 topic="Server Send presence informations" anchor='server_send_presence'>
        <p>Once the "presence" permission is granted, the server send presence informations:</p>
<example caption='server receives new presence from Juliet'><![CDATA[
<presence from='juliet@capulet.lit/balcony'
          id='presence1'
          xml:lang='en'>
    <show>chat</show>
    <status>Staying on the balcony</status>
</presence>
]]></example>

<example caption='server redirects presence to privileged entity'><![CDATA[
<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>
]]></example>

    </section2>

    <section2 topic='Roster Presence' anchor='roster_presence'>
        <p>In addition to "<link url='#managed_ent_presence'>managed entity presence</link>", 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).</p>
        <p>As for other permissions, the access in granted in server's configuration, but there is a additional restriction: the privileged entity MUST have read permission on roster namespace (i.e. 'type' attribute in allowed &lt;perm&gt; of namespace <em>jabber:iq:roster</em> MUST have a value of either <strong>get</strong> or <strong>both</strong>).</p>
    <p>If the delegation is granted, the server MUST send to the privileged entity every presence information that the privileged entity is receiving. Having "roster" type for "presence" permission imply that you have also implicitly "managed_entity" type.</p><p>The server MUST reject the permission if the privileged entity doesn't have read permission on roster namespace.</p>
    <p>Note: this permission should be given carefully, as it gives access to presence of potentially a lot of entities to the privileged entity (see <link url='#security'>security considerations</link>).</p>
    </section2>
            
    <section2 topic='Advertising Permission' anchor='advertise_roster_presence'>
        <p>Server advertise roster "presence" permission in the same way as for other permissions, except that the 'namespace' attribute has the value of "presence", and the 'type' attribute has a value of "roster"</p>
        <example caption='Server Advertise Roster, Message, Managed Entity Presence and Roster Presence Privileges'><![CDATA[
<message from='capulet.net' to='pubub.capulet.lit' id='54321'>
    <privilege xmlns='urn:xmpp:privilege:0'>
        <perm namespace='jabber:iq:roster' type='both'/>
        <perm namespace='message'/>
        <perm namespace='presence' type='roster'/>
    </privilege>
</message>
]]></example>
<p>Note the presence of <em>jabber:iq:roster</em> permission request.</p>
    </section2>

    <section2 topic="Privileged Entity Receive Roster Presences" anchor='priv_rec_roster_presence'>
<example caption="server receives new presence from Romeo, which is in Juliet's roster"><![CDATA[
<presence from='romeo@montaigu.lit/orchard'/>
]]></example>
<example caption='server sends the presence as usually, but also to the privileged entity'><![CDATA[
<presence from='romeo@montaigu.lit/orchard'
          to='juliet@capulet.lit'/>
<presence from='romeo@montaigu.lit/orchard'
          to='pubsub.capulet.lit'/>
]]></example>
</section2>
</section1>

<section1 topic='Security Considerations' anchor='security'>
    <ol>
        <li>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.</li>
        <li><link url='#roster_presence'>Roster presence</link> is particulary sensitive, because presence informations of whole rosters are shared.</li>
    </ol>
</section1>

<section1 topic='IANA Considerations' anchor='iana'>
  <p>This document requires no interaction with &IANA;.</p>
</section1>

<section1 topic='XMPP Registrar Considerations' anchor='registrar'>
  <section2 topic='Protocol Namespaces' anchor='ns'>
    <p>The &REGISTRAR; includes 'urn:xmpp:privilege:0' in its registry of protocol namespaces (see &NAMESPACES;).</p>
    <ul>
      <li>urn:xmpp:privilege:0</li>
    </ul>
  </section2>
  <section2 topic='Protocol Versioning' anchor='registrar-versioning'>
    &NSVER;
  </section2>
</section1>

<section1 topic='XML Schema' anchor='schema'>
  <code><![CDATA[
<?xml version='1.0' encoding='UTF-8'?>

<xs:schema
    xmlns:xs='http://www.w3.org/2001/XMLSchema'
    targetNamespace='urn:xmpp:privilege:0'
    xmlns='urn:xmpp:privilege:0'
    elementFormDefault='qualified'>

  <xs:element name='privilege'>
      <xs:complexType>
          <xs:element name='perm'
                      maxOccurs='unbounded'>
              <xs:complexType>
                  <xs:attribute name='namespace' use='required' type='xs:string'/>
                      <xs:simpleType base='xs:NMTOKEN'>
                          <xs:enumeration value='jabber:iq: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>
    ]]></code>
</section1>

<section1 topic='Acknowledgements' anchor='acks'>
  <p>Thanks to Sergey Dobrov, Dave Cridland, Steven Lloyd Watkin, Lance Stout and Johannes Hund for their feedbacks. Thanks to Adrien Cossa for his typos/style corrections.</p>
  <p>Privileged entity was initialy written to be a generic identity based access control (IBAC) which allows an entity to access sensitive data. After <link url='http://mail.jabber.org/pipermail/standards/2014-December/029378.html'>a discussion on standard mailing list</link>, 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.</p>

</section1>

</xep>