mirror of
https://github.com/moparisthebest/xeps
synced 2024-11-10 03:15:00 -05:00
373 lines
20 KiB
XML
373 lines
20 KiB
XML
<?xml version='1.0' encoding='UTF-8'?>
|
|
<!DOCTYPE xep SYSTEM 'xep.dtd' [
|
|
<!ENTITY % ents SYSTEM 'xep.ent'>
|
|
%ents;
|
|
]>
|
|
<?xml-stylesheet type='text/xsl' href='xep.xsl'?>
|
|
<xep>
|
|
<header>
|
|
<title>Pre-Authenticated Roster Subscription</title>
|
|
<abstract>This document defines a protocol and URI scheme for pre-authenticated roster links that allow a third party to automatically obtain the user's presence subscription. The goal of this is to make onboarding of new XMPP IM contacts as easy as possible.</abstract>
|
|
&LEGALNOTICE;
|
|
<number>0379</number>
|
|
<status>Experimental</status>
|
|
<type>Standards Track</type>
|
|
<sig>Standards</sig>
|
|
<approver>Council</approver>
|
|
<dependencies>
|
|
<spec>XMPP Core</spec>
|
|
<spec>RFC 5122</spec>
|
|
<spec>XEP-0147</spec>
|
|
</dependencies>
|
|
<supersedes/>
|
|
<supersededby/>
|
|
<shortname>pars</shortname>
|
|
<author>
|
|
<firstname>Georg</firstname>
|
|
<surname>Lukas</surname>
|
|
<email>georg@op-co.de</email>
|
|
<jid>georg@yax.im</jid>
|
|
</author>
|
|
<revision>
|
|
<version>0.1.0</version>
|
|
<date>2016-07-20</date>
|
|
<initials>gl (XEP Editor: ssw)</initials>
|
|
<remark><p>First draft.</p></remark>
|
|
</revision>
|
|
</header>
|
|
<section1 topic='Introduction' anchor='intro'>
|
|
<p>Romeo is an active XMPP IM (Instant Messaging) user. He convinces Juliet
|
|
(who doesn't have an XMPP account yet) to install a client and
|
|
register with some server. Now, Romeo only needs to create a mutual
|
|
presence subscription with her, without yet knowing her JID.</p>
|
|
<p>This specification allows Romeo to create an out-of-band link (URI) which,
|
|
when opened in Juilet's (or another user's) client, will:</p>
|
|
<ul>
|
|
<li>Add Romeo to Juliet's roster (with a display name optionally specified by Romeo)</li>
|
|
<li>Add Juliet to Romeo's roster (without a pre-defined display name)</li>
|
|
<li>Establish a mutual presence subscription between Romeo and Juliet</li>
|
|
</ul>
|
|
<p>The perceivable effect is that with a single click, Romeo and Juliet
|
|
become "friends" in terms of XMPP presence subscription.</p>
|
|
</section1>
|
|
<section1 topic='Requirements' anchor='reqs'>
|
|
<p>This specification makes use of XMPP URIs. The basic URI scheme for XMPP
|
|
is defined in &rfc5122; and extended in &xep0147; to support different
|
|
actions like "roster" for roster addition and "subscribe" for presence
|
|
subscription.
|
|
</p>
|
|
</section1>
|
|
<section1 topic='Pre-Authenticated Roster Subscription' anchor='pars'>
|
|
<p>The process of mutual roster addition and subscription involves multiple
|
|
steps:</p>
|
|
<ol>
|
|
<li>Generation of invitation link</li>
|
|
<li>Out-of-band transmission and presentation of the link</li>
|
|
<li>Subcription request to the user by the link receiver (new contact)</li>
|
|
<li>Approval by the user and mutual subscription request</li>
|
|
<li>Approval by the new contact</li>
|
|
</ol>
|
|
<p>The general idea of the protocol and the details of the individual steps
|
|
are outlined in the following.</p>
|
|
<section2 topic='General Idea' anchor='general_idea'>
|
|
<p>As Romeo doesn't know Juliet's JID, he needs to send an out-of-band
|
|
invitation. Later, his client needs to match an incoming subscription
|
|
request to this invitation, so it can perform a secure automatic roster
|
|
addition and subscription approval. This matching is accomplished by
|
|
means of an authentication token, which is generated by Romeo's client,
|
|
added to the invitation link and then carried over into the subscription
|
|
request eventually made by Juliet's client. Romeo's client can then
|
|
compare the token received in a subscription request to the list of
|
|
issued tokens, and automatically approve the subscription.</p>
|
|
<code caption='Successful PARS Protocol Flow'><![CDATA[
|
|
Romeo mongatague.net capulet.net Juliet
|
|
| | | |
|
|
| Send out-of-band invitation link |
|
|
| (xmpp:romeo@montague.net?preauth=token) |
|
|
|- - - - - - - - - - - - - - - - - - - - - - ->|
|
|
| | | roster add |
|
|
| | |<--------------|
|
|
| presence subscription request w/ token |
|
|
| <presence><preauth token="..."/></presence> |
|
|
|<---------------------------------------------|
|
|
| (token validation check) | |
|
|
| presence subscribed | |
|
|
|--------------------------------------------->|
|
|
| roster add | | |
|
|
|------------->| | |
|
|
| presence subscription request| |
|
|
|--------------------------------------------->|
|
|
| | (auto approval) |
|
|
| | presence subscribed |
|
|
|<---------------------------------------------|
|
|
]]></code>
|
|
</section2>
|
|
<section2 topic='Generation of Invitation Link' anchor='link_generation'>
|
|
<p>Whenever Romeo wishes to invite somebody to his roster, his client will
|
|
generate an invitation link that contains a new authentication token.
|
|
This document extends the "roster" URI action defined in <cite>XEP-0147</cite> with
|
|
a new key-value parameter named "preauth" to store the generated token.
|
|
Romeo's client will create an <strong>xmpp:</strong> link containing Romeo's JID, the
|
|
"roster" action, the "preauth" parameter with the token value, and
|
|
optionally a "name" parameter with the suggested display name.
|
|
</p>
|
|
<example caption='Invitation Link with Roster Action and Authentication Token'><![CDATA[
|
|
xmpp:romeo@montague.net?roster;preauth=1tMFqYDdKhfe2pwp;name=Romeo%20Montague
|
|
]]></example>
|
|
<p>
|
|
If the "preauth" parameter is present, the processing client is supposed
|
|
not only to add the user to the roster, but also to automatically send a
|
|
subscription request containing the authentication token.
|
|
</p>
|
|
|
|
<p></p>
|
|
|
|
<p><strong>Server-side implementation:</strong> it is
|
|
possible (but out-of-scope for this document), to let the user's server
|
|
handle generation of links as well as automatic approval of qualified
|
|
subscription requests. This requires an additional mechanism to query the
|
|
server for new (and possibly also for pending) invitation links.</p>
|
|
|
|
</section2>
|
|
|
|
<section2 topic='Out-of-band transmission and presentation of the link' anchor='link_transmission'>
|
|
<p>As Romeo doesn't know Juliet's JID in advance, he needs to use an out-of-band method (like e-mail, QR codes or NFC) to transmit the invitation link to Juliet. While these methods allow transmission of <strong>xmpp:</strong> URIs, there is no mechanism to ensure that Juliet actually has a client installed that can open the URI.</p>
|
|
<p>One way to solve this problem is to present Juliet with a web-based landing page that contains the following elements:</p>
|
|
<ul>
|
|
<li>A short text that this is an XMPP invitation from Romeo.</li>
|
|
<li>A client recommendation (based on the detected web browser) with download links.</li>
|
|
<li>A prominent button that activates the actual <strong>xmpp:</strong> link.</li>
|
|
</ul>
|
|
<p>There are multiple options where such a landing page could be hosted:</p>
|
|
<ol>
|
|
<li><strong>XSF:</strong> a central place would provide a common ground
|
|
for a curated client list and ensure long-term availability. However,
|
|
the operator would be able to collect meta-data and abuse authentication tokens.</li>
|
|
<li><strong>Client developer:</strong> the developer of Romeo's client can
|
|
provide a landing page for invitation requests created with this
|
|
client. This is a feasible short-term solution and allows to recommend
|
|
the same client as used by the link sender. However, it shares the
|
|
privacy objections of the XSF solution and can not guarantee
|
|
long-term availability of the service. If the client development shuts
|
|
down, invitation links created with the client will cease working.</li>
|
|
<li><strong>User's server:</strong> this is the optimal long-term
|
|
solution, as the user's server is already entrusted with the relevant
|
|
meta-data and will exist at least as long as the user's account on that
|
|
server. However, this requires an additional server component to query
|
|
for invitation URIs and a web server hosting the landing page.
|
|
Furthermore, the server operator needs to maintain the list of
|
|
recommended clients.</li>
|
|
</ol>
|
|
<example caption='Developer-Hosted Landing Page Generated with yaxim'><![CDATA[
|
|
https://yax.im/i/romeo/montague.net/1tMFqYDdKhfe2pwp/Romeo+Montague
|
|
]]></example>
|
|
<p>A possible screen representation of the landing page would be:</p>
|
|
<div class="example">
|
|
<p><strong><em>Romeo Montague</em> has invited you to chat</strong></p>
|
|
|
|
<p><strong><link url='xmpp:romeo@montague.net?roster;preauth=1tMFqYDdKhfe2pwp;name=Romeo%20Montague'>Add <em>Romeo Montague</em></link></strong></p>
|
|
<p>If this link does not work, you need to install and configure
|
|
an XMPP client. Please visit this page again afterwards. Choose one of
|
|
these for your <em>Tomato OS</em>:</p>
|
|
<ul>
|
|
<li><strong>JuicyXMPP</strong> (link to XMPP client)</li>
|
|
<li><strong>VegetableChat</strong> (link to XMPP client)</li>
|
|
</ul>
|
|
<p>Check the <link url='http://xmpp.org/software/clients.html'>full list of XMPP clients</link>.</p>
|
|
<p>No further action is required if you do not know <em>Romeo Montague</em> or do not want to chat with them.</p>
|
|
<p>XMPP is a provider-independent form of instant messaging. That means
|
|
you can pick from many different clients and have a free choice of
|
|
server operators to communicate with <em>Romeo Montague</em>.</p>
|
|
|
|
</div>
|
|
|
|
</section2>
|
|
|
|
<section2 topic='Subcription request to the user by the link receiver (new contact)' anchor='link_transmission'>
|
|
<p>When Juliet opens the <strong>xmpp:</strong> URI (or the according client-supported
|
|
landing page URI) in her client, the client should perform the usual
|
|
roster addition action, i.e. display a dialog allowing to edit the entry
|
|
or to cancel the process. If Juliet completes the roster addition, the
|
|
client SHOULD also send a subscription request to Romeo. This request
|
|
SHOULD contain a 'preauth' element containing the authentication token
|
|
from the invitation link.
|
|
</p>
|
|
<example caption='Subscription Request with Pre-Authenticated Roster Subscription Element'><![CDATA[
|
|
<presence to='romeo@montague.net' type='subscribe'>
|
|
<preauth xmlns='urn:xmpp:pars:0' token='1tMFqYDdKhfe2pwp' />
|
|
</presence>
|
|
]]></example>
|
|
<p>If Juliet's server supports <link
|
|
url='http://xmpp.org/rfcs/rfc6121.html#sub-preapproval'>subscription
|
|
pre-approval</link>, the client SHOULD additionally pre-approve Romeo:
|
|
</p>
|
|
<example caption='Juliet Pre-approves Romeo'><![CDATA[
|
|
<presence to='romeo@montague.net' type='subscribed' />
|
|
]]></example>
|
|
<p>If Juliet's server does not indicate pre-approval support, her client
|
|
SHOULD store Romeo's JID in a local auto-approval whitelist, together
|
|
with an appropriate expiration time.
|
|
</p>
|
|
</section2>
|
|
|
|
<section2 topic='Approval by the User and Mutual Subscription Request' anchor='sub_approval'>
|
|
<p>When Romeo's client receives a subscription request containing a
|
|
'preauth' element, it needs to extract the authentication token and
|
|
check if the token is a valid one and was previously issued by the client
|
|
(see security considerations below).</p>
|
|
<example caption='Subscription Request With Tokens Received by Romeo'><![CDATA[
|
|
<presence to='romeo@montague.net' from='juliet@capulet.net' type='subscribe'>
|
|
<preauth xmlns='urn:xmpp:pars:0' token='1tMFqYDdKhfe2pwp' />
|
|
</presence>
|
|
]]></example>
|
|
<p>If the token is considered valid, the client SHOULD automatically approve
|
|
the subscription request, add the sender of the subscription request to
|
|
the roster and send a subscription request of its own.</p>
|
|
<example caption='Automatic Approval and Response Subscription Request'><![CDATA[
|
|
<presence to='juliet@capulet.net' type='subscribed' />
|
|
<presence to='juliet@capulet.net' type='subscribe' />
|
|
]]></example>
|
|
|
|
</section2>
|
|
|
|
<section2 topic='Approval by the New Contact' anchor='sub_mutual_approval'>
|
|
<p>If Juliet's server support pre-approval, it will automatically handle the
|
|
incoming subscription request and issue a roster push. Otherwise, Juliet's
|
|
client will receive the subscription request:</p>
|
|
<example caption='Mutual Subscription Request'><![CDATA[
|
|
<presence from='romeo@montague.net' to='juliet@capulet.net' type='subscribe' />
|
|
]]></example>
|
|
<p>Juliet's client SHOULD check the subscription request sender JID against
|
|
the whitelist, and either automatically approve the request or display an
|
|
according notification to Juliet.</p>
|
|
|
|
</section2>
|
|
</section1>
|
|
<section1 topic='Business Rules' anchor='rules'>
|
|
<section2 topic='Fallback to manual process' anchor='rules_fallback'>
|
|
<p>An implementation of this protocol MUST allow for a "graceful
|
|
degradation" to the manual subscription approval process. If a client
|
|
receives a malformed or unknown 'preauth' token, it MUST ignore it and act
|
|
as if no preauth token was contained.</p>
|
|
</section2>
|
|
|
|
<section2 topic='No expectaion of immediate approval' anchor='rules_expectation'>
|
|
<p>When sending a pre-authenticated subscription request, the contact's
|
|
client MUST NOT expect an immediate successful approval. If the user's
|
|
issuing client is currently offline, or if the token has expired, a manual
|
|
approval will be performed. Therefore, the contact's client should use the
|
|
same mechanism as before to indicate an unidirectional subscription.
|
|
</p>
|
|
</section2>
|
|
|
|
<section2 topic='Use of multiple clients' anchor='rules_multiclient'>
|
|
<p>If a user is logged in with multiple clients, some of their clients will
|
|
receive a subscription request with an unknown token. In this case, a client
|
|
MAY delay the user notification for a short time, to allow another logged-in
|
|
client to automatically handle the subscription request.</p>
|
|
</section2>
|
|
|
|
<section2 topic='Opening the landing page in an app' anchor='rules_multiclient'>
|
|
<p>Some mobile device platforms allow an app to register itself as a
|
|
handler for cetain URIs. This allows an XMPP client to register for <strong>xmpp:</strong>
|
|
URIs, but also to redirect handling of cetain HTTP/HTTPS URIs. A mobile
|
|
client SHOULD register for the associated landing page URIs and properly
|
|
handle the contained invitations. For example, the yaxim client should
|
|
register a handler for <strong>https://yax.im/i/*</strong>, and present
|
|
the "Add to roster" dialog if such a link is opened. A client MAY register
|
|
for the landing page URIs of other providers after obtaining the
|
|
operators' approval.
|
|
</p>
|
|
</section2>
|
|
</section1>
|
|
<section1 topic='Security Considerations' anchor='security'>
|
|
<section2 topic='Token Generation' anchor='security_token'>
|
|
<p>As the authentication token grants automatic addition to
|
|
Romeo's roster and automatic approval of presence subscription,
|
|
the token SHOULD be created with a cryptographically secure random
|
|
number generator <note>See for example <link
|
|
url='https://lwn.net/Articles/606141/'><tt>getrandom(2)</tt></link>,
|
|
<link
|
|
url='https://docs.oracle.com/javase/8/docs/api/java/security/SecureRandom.html'><tt>SecureRandom</tt></link>
|
|
or <tt>/dev/urandom</tt>. More information about the randomness
|
|
requirements for security can be found in &rfc4086;</note> and
|
|
provide sufficient entropy to make brute-force attacks
|
|
infeasible. It is suggested to generate at least 80 bits of
|
|
entropy, and to use an encoding that can be easily encoded as part
|
|
of an URI (e.g. Base-32).</p> <p>It is possible to use a different token
|
|
generation scheme like <cite>SAML</cite><note>Security Assertion Markup
|
|
Language (SAML) <<link url='https://www.oasis-open.org/standards#samlv2.0'>https://www.oasis-open.org/standards#samlv2.0</link>></note>
|
|
or JWT (<cite><link url='http://tools.ietf.org/html/rfc7519'>RFC
|
|
7519</link></cite><note>RFC 7519: JSON Web Token (JWT) <<link url='http://tools.ietf.org/html/rfc7519'>http://tools.ietf.org/html/rfc7519</link>></note>). In
|
|
such a case, the issuer must ensure a comparable security level
|
|
and limit token reuse.</p>
|
|
</section2>
|
|
<section2 topic='Checking Token Validity' anchor='security_validity'>
|
|
<p>To limit the potential for abuse, the token SHOULD be limited in as follows:</p>
|
|
<ul>
|
|
<li><strong>Usage:</strong> in the typical scenario, each token may only
|
|
be used once. While it is possible for a client to generate a token for
|
|
multiple uses (like for embedding it in a contact card), the
|
|
conventional manual roster management should be used for public
|
|
invitation links.</li>
|
|
<li><strong>Time:</strong> each token MUST have a limited validity time.
|
|
As the token is transmitted out-of-band, it should provide sufficient
|
|
reaction time, e.g. one week. This time limit also allows the issuer to
|
|
delete expired tokens.</li>
|
|
<li><strong>Identity:</strong> if the JID of the token receiver is known
|
|
in advance, the token sender MUST NOT allow a different JID to redeem
|
|
this token.</li>
|
|
</ul>
|
|
<p>If a token is considered invalid (due to failing any of the above
|
|
conditions, or for other reasons), a client MUST fall back to manual
|
|
roster addition and manual subscription approval.
|
|
</p>
|
|
</section2>
|
|
<section2 topic='Invitation Link Validity' anchor='security_link'>
|
|
<p>The invitation link that is generated by Romeo's client is considered a
|
|
personal invitation link for a single person. This, and the fact that the
|
|
link can only be used once, should be indicated by the client to Romeo.
|
|
</p>
|
|
</section2>
|
|
<section2 topic='Interception of Links' anchor='security_intercept'>
|
|
<p>A Monkey-in-the-Middle attacker who gains access to the invitation link
|
|
can manipulate its fields or redeem the link themselves. However, this is
|
|
true for all communication performed using the chosen medium and is out of
|
|
scope for this document.</p>
|
|
<p>Ideally, Romeo's client should highlight automatically-added roster items
|
|
and provide an easy mechanism to remove them and cancel their
|
|
subscription.</p>
|
|
</section2>
|
|
<section2 topic='Display Names' anchor='security_token'>
|
|
<p>An attacker can lure the user by providing an invitation link with a
|
|
'name' parameter that does not match the JID. Therefore, a client SHOULD
|
|
always display both the JID and the proposed display name when adding a
|
|
roster item.</p>
|
|
<p>When the user's client automatically approves a subscription, it SHOULD
|
|
add the new contact to the roster without a 'name' or with the 'name'
|
|
equal to the JID, to prevent impersonation attacks.</p>
|
|
</section2>
|
|
</section1>
|
|
<section1 topic='IANA Considerations' anchor='iana'>
|
|
<p>This document requires no interaction with &IANA;.</p>
|
|
</section1>
|
|
<section1 topic='XMPP Registrar Considerations' anchor='registrar'>
|
|
<p>Include the "urn:xmpp:pars:0" namespace in the registry of protocol
|
|
namespaces. Include "preauth" as an additional key-value parameter to the
|
|
roster query action.</p>
|
|
<code caption='New Roster Query Action Parameter'><![CDATA[
|
|
<querytype>
|
|
<name>roster</name>
|
|
...
|
|
<key>
|
|
<name>preauth</name>
|
|
<desc>the token used to obtain an automatic approval from the target JID</desc>
|
|
</key>
|
|
</querytype>
|
|
]]></code>
|
|
</section1>
|
|
<section1 topic='XML Schema' anchor='schema'>
|
|
<p>REQUIRED for protocol specifications.</p>
|
|
</section1>
|
|
</xep>
|