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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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<title>draft: OpenID OAuth Extension</title>
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<table summary="layout" class="TOCbug" align="right" cellpadding="0" cellspacing="2"><tbody><tr><td class="TOCbug"><a href="#toc"> TOC </a></td></tr></tbody></table>
<table summary="layout" border="0" cellpadding="0" cellspacing="0" width="66%"><tbody><tr><td><table summary="layout" border="0" cellpadding="2" cellspacing="1" width="100%">
<tbody><tr><td class="header">draft</td><td class="header">D. Balfanz</td></tr>
<tr><td class="header"> </td><td class="header">B. de Medeiros</td></tr>
<tr><td class="header"> </td><td class="header">Google</td></tr>
<tr><td class="header"> </td><td class="header">D. Recordon</td></tr>
<tr><td class="header"> </td><td class="header">Six Apart</td></tr>
<tr><td class="header"> </td><td class="header">J. Smarr</td></tr>
<tr><td class="header"> </td><td class="header">Plaxo</td></tr>
<tr><td class="header"> </td><td class="header">A. Tom</td></tr>
<tr><td class="header"> </td><td class="header">Yahoo</td></tr>
<tr><td class="header"> </td><td class="header">January 7, 2009</td></tr>
</tbody></table></td></tr></tbody></table>
<h1><br>OpenID OAuth Extension</h1>
<h3>Abstract</h3>
<p>This draft describes a mechanism to combine an OpenID
authentication request with the approval of an OAuth request token.
</p><a name="toc"></a><br><hr>
<h3>Table of Contents</h3>
<p class="toc">
<a href="#anchor1">1.</a>
Requirements notation<br>
<a href="#anchor2">2.</a>
Terminology<br>
<a href="#anchor3">3.</a>
Purpose of this Specification<br>
<a href="#anchor4">4.</a>
Overview<br>
<a href="#namespace">5.</a>
Extension Namespace<br>
<a href="#anchor5">6.</a>
Discovery<br>
<a href="#Registered">7.</a>
Before Requesting Authentication - Registration<br>
<a href="#AuthReq">8.</a>
Requesting Authentication<br>
<a href="#anchor6">9.</a>
Authorizing the OAuth Request<br>
<a href="#AuthResp">10.</a>
Responding to Authentication Requests<br>
<a href="#AuthTokenReq">11.</a>
Obtaining the Access Token<br>
<a href="#anchor7">12.</a>
General Considerations<br>
<a href="#anchor8">13.</a>
Security Considerations<br>
<a href="#rfc.references1">14.</a>
Normative References<br>
<a href="#rfc.authors">§</a>
Authors' Addresses<br>
</p>
<br clear="all">
<a name="anchor1"></a><br><hr>
<table summary="layout" class="TOCbug" align="right" cellpadding="0" cellspacing="2"><tbody><tr><td class="TOCbug"><a href="#toc"> TOC </a></td></tr></tbody></table>
<a name="rfc.section.1"></a><h3>1.
Requirements notation</h3>
<p>The key words "MUST", "MUST NOT", "REQUIRED", "SHALL",
"SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY",
and "OPTIONAL" in this document are to be interpreted as
described in <a class="info" href="#RFC2119">[RFC2119]<span> (</span><span class="info">Bradner, S., “Key words for use in RFCs to Indicate Requirement Levels,” March 1997.</span><span>)</span></a>.
</p>
<a name="anchor2"></a><br><hr>
<table summary="layout" class="TOCbug" align="right" cellpadding="0" cellspacing="2"><tbody><tr><td class="TOCbug"><a href="#toc"> TOC </a></td></tr></tbody></table>
<a name="rfc.section.2"></a><h3>2.
Terminology</h3>
<p>Terms <em>emphasized</em> are pre-defined in either the
<a class="info" href="#OpenID">[OpenID]<span> (</span><span class="info">Openid.net, “OpenID Authentication 2.0 - Final,” December 2007.</span><span>)</span></a>
or the <a class="info" href="#OAuth">[OAuth]<span> (</span><span class="info">OAuth Core Workgroup, “OAuth Core 1.0,” December 2007.</span><span>)</span></a> specifications.
</p>
<blockquote class="text"><dl>
<dt>Combined Consumer:</dt>
<dd>
A web service that is simultaneously an OpenID
<em>Relying Party (RP)</em> and
an OAuth <em>Consumer.</em>
</dd>
<dt>Combined Provider:</dt>
<dd>A web service that is simultaneously
an OpenID <em>Identity Provider (OP)</em> and
an OAuth <em>Service Provider (SP).</em>
</dd>
</dl></blockquote><p>
</p>
<a name="anchor3"></a><br><hr>
<table summary="layout" class="TOCbug" align="right" cellpadding="0" cellspacing="2"><tbody><tr><td class="TOCbug"><a href="#toc"> TOC </a></td></tr></tbody></table>
<a name="rfc.section.3"></a><h3>3.
Purpose of this Specification</h3>
<p>The OpenID OAuth Extension describes how to make the OpenID
Authentication and OAuth Core specifications work well
together. In its current form, it addresses the use case where
the OpenID Provider and OAuth Service Provider are the same
service. To provide good user experience, it is important to
present, to the user, a combined authentication and
authorization screen for the two protocols.
</p>
<p>This extension describes how to embed an OAuth approval
request into an OpenID authentication request to permit
combined user approval. For security reasons, the OAuth access
token is not returned in the OpenID authentication response.
Instead a mechanism to obtain the access token is provided.
</p>
<a name="anchor4"></a><br><hr>
<table summary="layout" class="TOCbug" align="right" cellpadding="0" cellspacing="2"><tbody><tr><td class="TOCbug"><a href="#toc"> TOC </a></td></tr></tbody></table>
<a name="rfc.section.4"></a><h3>4.
Overview</h3>
<p>Unlike standard OAuth (<a class="info" href="#OAuth">[OAuth]<span> (</span><span class="info">OAuth Core Workgroup, “OAuth Core 1.0,” December 2007.</span><span>)</span></a>), the OpenID
OAuth Extension does not provision request tokens in a
server-to-server request from the Combined Consumer to the
request token endpoint at the Combined Provider. Instead, the
Combined Provider returns an already-approved request token to
the Combined Consumer as part of the OpenID authentication
response.
</p>
<p>
The Combined Consumer then exchanges the request token for an
access token at the access token endpoint of the Combined
Provider, following standard OAuth practice.
</p>
<a name="namespace"></a><br><hr>
<table summary="layout" class="TOCbug" align="right" cellpadding="0" cellspacing="2"><tbody><tr><td class="TOCbug"><a href="#toc"> TOC </a></td></tr></tbody></table>
<a name="rfc.section.5"></a><h3>5.
Extension Namespace</h3>
<p>This protocol is an extension as defined by Section 12 of
<a class="info" href="#OpenID">[OpenID]<span> (</span><span class="info">Openid.net, “OpenID Authentication 2.0 - Final,” December 2007.</span><span>)</span></a>. The namespace URI for this extension is
"http://specs.openid.net/extensions/oauth/1.0".
</p>
<p>All OpenID messages that contain an OpenID OAuth Extension element
MUST contain the following extension namespace declaration:
</p><div style="display: table; width: 0pt; margin-left: 3em; margin-right: auto;"><pre>openid.ns.<alias>=http://specs.openid.net/extensions/oauth/1.0</pre></div>
<p>
The actual extension namespace alias is determined by the party
composing the message in such a manner as to avoid conflicts
among multiple extensions. Throughout this document "oauth" is
used as an example for the extension namespace alias.
</p>
<a name="anchor5"></a><br><hr>
<table summary="layout" class="TOCbug" align="right" cellpadding="0" cellspacing="2"><tbody><tr><td class="TOCbug"><a href="#toc"> TOC </a></td></tr></tbody></table>
<a name="rfc.section.6"></a><h3>6.
Discovery</h3>
<p>Discovery of the OpenID OAuth Extension is achieved via the
mechanism described in <a class="info" href="#OpenID">[OpenID]<span> (</span><span class="info">Openid.net, “OpenID Authentication 2.0 - Final,” December 2007.</span><span>)</span></a>. The OpenID OAuth
Extension namespace
"http://specs.openid.net/extensions/oauth/1.0" SHOULD be listed
as an <xrd:Type> child element of the <xrd:Service>
element in the XRDS discovery document.
</p>
<a name="Registered"></a><br><hr>
<table summary="layout" class="TOCbug" align="right" cellpadding="0" cellspacing="2"><tbody><tr><td class="TOCbug"><a href="#toc"> TOC </a></td></tr></tbody></table>
<a name="rfc.section.7"></a><h3>7.
Before Requesting Authentication - Registration</h3>
<p>The Combined Consumer and the Combined Provider agree on a
consumer key and consumer secret (see <a class="info" href="#OAuth">[OAuth]<span> (</span><span class="info">OAuth Core Workgroup, “OAuth Core 1.0,” December 2007.</span><span>)</span></a>).
</p>
<p>The Combined Provider SHOULD in addition obtain, from the
Combined Consumer, a list of valid OpenID realms that the
Combined Consumer may use in subsequent authentication
requests. The Combined Provider SHOULD verify that the Combined
Consumer is authorized to use those realms.
</p>
<a name="AuthReq"></a><br><hr>
<table summary="layout" class="TOCbug" align="right" cellpadding="0" cellspacing="2"><tbody><tr><td class="TOCbug"><a href="#toc"> TOC </a></td></tr></tbody></table>
<a name="rfc.section.8"></a><h3>8.
Requesting Authentication</h3>
<p>When requesting OpenID Authentication via the protocol mode
"checkid_setup" or "checkid_immediate", this extension can be
used to request that the end user authorize an OAuth access token at
the same time as an OpenID authentication. This is done by
sending the following parameters as part of the OpenID
request. (Note that the use of "oauth" as part of the
parameter names here and in subsequent sections is just an
example. See <a class="info" href="#namespace">Section 5<span> (</span><span class="info">Extension Namespace</span><span>)</span></a> for details.)
</p>
<blockquote class="text"><dl>
<dt>openid.ns.oauth</dt>
<dd>
REQUIRED. Value:
"http://specs.openid.net/extensions/oauth/1.0".
</dd>
<dt>openid.oauth.consumer</dt>
<dd>
REQUIRED. Value: The consumer key agreed upon in <a class="info" href="#Registered">Section 7<span> (</span><span class="info">Before Requesting Authentication - Registration</span><span>)</span></a>.
</dd>
<dt>openid.oauth.scope</dt>
<dd>
OPTIONAL. Value: A string that encodes, in a way possibly specific to
the Combined Provider, one or more scopes for the OAuth
token expected in the authentication response.
</dd>
</dl></blockquote><p>
</p>
<a name="anchor6"></a><br><hr>
<table summary="layout" class="TOCbug" align="right" cellpadding="0" cellspacing="2"><tbody><tr><td class="TOCbug"><a href="#toc"> TOC </a></td></tr></tbody></table>
<a name="rfc.section.9"></a><h3>9.
Authorizing the OAuth Request</h3>
<p>If the OpenID OAuth Extension is present in the authentication
request, the Combined Provider SHOULD verify that the consumer
key passed in the request is authorized to be used for the
realm passed in the request. If this verification succeeds, the
Combined Provider SHOULD determine that delegation of access
from a user to the Combined Consumer has been requested.
</p>
<p>The Combined Provider SHOULD NOT issue an approved request
token unless it has user consent to perform such delegation.
</p>
<a name="AuthResp"></a><br><hr>
<table summary="layout" class="TOCbug" align="right" cellpadding="0" cellspacing="2"><tbody><tr><td class="TOCbug"><a href="#toc"> TOC </a></td></tr></tbody></table>
<a name="rfc.section.10"></a><h3>10.
Responding to Authentication Requests</h3>
<p>If the OpenID authentication request cannot be fulfilled (either in
failure mode "setup_needed" or "cancel" as in Sections 10.2.1 and 10.2.2
of <a class="info" href="#OpenID">[OpenID]<span> (</span><span class="info">Openid.net, “OpenID Authentication 2.0 - Final,” December 2007.</span><span>)</span></a>) then the OAuth request SHOULD be considered
to fail and the Provider MUST NOT send any OpenID OAuth Extension values in the
response.
</p>
<p>The remainder of this section specifies how to handle the OAuth
request in cases when the OpenID authentication response is a positive
assertion (Section 10.1 of <a class="info" href="#OpenID">[OpenID]<span> (</span><span class="info">Openid.net, “OpenID Authentication 2.0 - Final,” December 2007.</span><span>)</span></a>).
</p>
<p>If the end user does wish to delegate access to the Combined Consumer,
the Combined Provider MUST include and MUST sign
the following parameters.
</p>
<blockquote class="text"><dl>
<dt>openid.ns.oauth</dt>
<dd>
REQUIRED. Identical value as defined in <a class="info" href="#AuthReq">Section 8<span> (</span><span class="info">Requesting Authentication</span><span>)</span></a>.
</dd>
<dt>openid.oauth.request_token</dt>
<dd>
REQUIRED. A user-approved request token.
</dd>
<dt>openid.oauth.scope</dt>
<dd>
OPTIONAL. A string that encodes, in a way possibly specific to
the Combined Provider, one or more scopes that the
returned request token is valid for. This will typically
indicate a subset of the scopes requested in <a class="info" href="#AuthReq">Section 8<span> (</span><span class="info">Requesting Authentication</span><span>)</span></a>.
</dd>
</dl></blockquote><p>
To note that the OAuth Authorization was declined or not valid,
the Combined Provider SHALL only respond with the parameter
"openid.ns.oauth".
</p>
<a name="AuthTokenReq"></a><br><hr>
<table summary="layout" class="TOCbug" align="right" cellpadding="0" cellspacing="2"><tbody><tr><td class="TOCbug"><a href="#toc"> TOC </a></td></tr></tbody></table>
<a name="rfc.section.11"></a><h3>11.
Obtaining the Access Token</h3>
<p>To exchange the request token for an access token, the
Combined Consumer follows Section 6.3.1 of
<a class="info" href="#OAuth">[OAuth]<span> (</span><span class="info">OAuth Core Workgroup, “OAuth Core 1.0,” December 2007.</span><span>)</span></a>, i.e., it sends an access token request
to the access token endpoint of the Combined Provider. It
SHALL use the following values to create the OAuth access
token request:
</p>
<blockquote class="text"><dl>
<dt>consumer key</dt>
<dd>
Combined Consumers use the consumer key they established with the
Combined Provider in <a class="info" href="#Registered">Section 7<span> (</span><span class="info">Before Requesting Authentication - Registration</span><span>)</span></a>.
</dd>
<dt>consumer secret</dt>
<dd>
Combined Consumers use the consumer secret they established with
the Combined Provider in <a class="info" href="#Registered">Section 7<span> (</span><span class="info">Before Requesting Authentication - Registration</span><span>)</span></a>.
</dd>
<dt>OAuth token</dt>
<dd>
Combined Consumers use the request token obtained in
<a class="info" href="#AuthResp">Section 10<span> (</span><span class="info">Responding to Authentication Requests</span><span>)</span></a>.
</dd>
<dt>OAuth token secret</dt>
<dd>
Combined Consumers use the empty string.
</dd>
</dl></blockquote><p>
</p>
<p>
The Combined Provider follows Section 6.3.2 to verify the
request and either issue the access token or send an error
response.
</p>
<a name="anchor7"></a><br><hr>
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<a name="rfc.section.12"></a><h3>12.
General Considerations</h3>
<p>The proposal takes the approach to insulate each protocol
from the other, both for backwards compatibility as
well as to enable OpenID and OAuth to evolve and incorporate additional
features without requiring reviews of the combined usage described here.
In particular:
</p>
<blockquote class="text"><dl>
<dt>OpenID full compatibility</dt>
<dd>The OpenID identity provider
(OP) MAY safely announce the endpoint supporting the OpenID OAuth Extension
to all relying parties, whether or not they support
the extension as well.
The use of a separate service-type announcement
for Combined Providers
endpoints provides a mechanism for auto-discovery
of OAuth capabilities by RPs.
</dd>
<dt>OAuth token compatibility</dt>
<dd>The OAuth tokens approved
via this mechanism MAY be used identically as tokens acquired through
alternative mechanisms (e.g., via standard OAuth) without requiring
special considerations either because of functionality or security
reasons.
</dd>
</dl></blockquote><p>
</p>
<a name="anchor8"></a><br><hr>
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<a name="rfc.section.13"></a><h3>13.
Security Considerations</h3>
<p>This proposal composes protocols that provide security
services (authentication in the case of OpenID, authorization
in the case of OAuth) with the intention that the combined
protocol provides both services simultaneously. Since security
is not a property generally preserved by composition, the
design takes the approach of encapsulating the OAuth flow
within OpenID in a modular way, and applies the general
rule-of-thumb of NOT introducing reliance on the security
properties of one protocol for the correctness of the
other. Ultimately, only public scrutiny and review can
incrementally provide confidence that the approach described
here is sound from a security perspective.
</p>
<p>The following security principles are reflected in this design:
</p>
<blockquote class="text"><dl>
<dt>No long-term OAuth secrets hit the browser</dt>
<dd>
The OAuth protocol was designed so that browser-mediated
communication is not used to transfer long-term secrets or
capabilities to access data.(Instead, server-to-server
calls are used to exchange such secrets). Combined
Providers can preserve this property by making the
request_token short-lived, since the request token will be
exchanged for an access token and secret over a
server-to-server call.
</dd>
<dt>Imposters cannot retrieve the OAuth access token</dt>
<dd>
While it is possible for a malicious party to fake an
OpenID request, including an OpenID request that includes
the OpenID OAuth Extension (the request is not signed, and
knowledge of the consumer key and realm is sufficient
to cause the Combined Provider to display an authorization
page for that realm/consumer), that malicious party would
have to have knowledge of the consumer secret to exchange
the request token for an access token. Note that while
secure under reasonable threat models, this is different
from standard OAuth: In standard OAuth, one needs
knowledge of both the consumer key and consumer secret
(or, alternatively, of a request token obtained through
knowledge of the consumer key and secret) to cause the
Service Provider to display an authorization page for that
consumer.
</dd>
</dl></blockquote><p>
</p>
<a name="rfc.references1"></a><br><hr>
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<h3>14. Normative References</h3>
<table border="0" width="99%">
<tbody><tr><td class="author-text" valign="top"><a name="OAuth">[OAuth]</a></td>
<td class="author-text"><a href="mailto:[email protected]">OAuth Core Workgroup</a>, “<a href="http://oauth.net/core/1.0/">OAuth Core 1.0</a>,” December 2007 (<a href="http://oauth.net/core/1.0/">HTML</a>).</td></tr>
<tr><td class="author-text" valign="top"><a name="OpenID">[OpenID]</a></td>
<td class="author-text"><a href="mailto:[email protected]">Openid.net</a>, “<a href="http://openid.net/specs/openid-authentication-2_0.html">OpenID Authentication 2.0 - Final</a>,” December 2007 (<a href="http://openid.net/specs/openid-authentication-2_0.html">HTML</a>, <a href="http://openid.net/specs/openid-authentication-2_0.txt">TXT</a>).</td></tr>
<tr><td class="author-text" valign="top"><a name="RFC2119">[RFC2119]</a></td>
<td class="author-text"><a href="mailto:[email protected]">Bradner, S.</a>, “<a href="http://tools.ietf.org/html/rfc2119">Key words for use in RFCs to Indicate Requirement Levels</a>,” BCP 14, RFC 2119, March 1997 (<a href="ftp://ftp.isi.edu/in-notes/rfc2119.txt">TXT</a>, <a href="http://xml.resource.org/public/rfc/html/rfc2119.html">HTML</a>, <a href="http://xml.resource.org/public/rfc/xml/rfc2119.xml">XML</a>).</td></tr>
</tbody></table>
<a name="rfc.authors"></a><br><hr>
<table summary="layout" class="TOCbug" align="right" cellpadding="0" cellspacing="2"><tbody><tr><td class="TOCbug"><a href="#toc"> TOC </a></td></tr></tbody></table>
<h3>Authors' Addresses</h3>
<table border="0" cellpadding="0" cellspacing="0" width="99%">
<tbody><tr><td class="author-text"> </td>
<td class="author-text">Dirk Balfanz (editor)</td></tr>
<tr><td class="author-text"> </td>
<td class="author-text">Google, Inc.</td></tr>
<tr><td class="author" align="right">Email: </td>
<td class="author-text"><a href="mailto:[email protected]">[email protected]</a></td></tr>
<tr cellpadding="3"><td> </td><td> </td></tr>
<tr><td class="author-text"> </td>
<td class="author-text">Breno de Medeiros (editor)</td></tr>
<tr><td class="author-text"> </td>
<td class="author-text">Google, Inc.</td></tr>
<tr><td class="author" align="right">Email: </td>
<td class="author-text"><a href="mailto:[email protected]">[email protected]</a></td></tr>
<tr cellpadding="3"><td> </td><td> </td></tr>
<tr><td class="author-text"> </td>
<td class="author-text">David Recordon (editor)</td></tr>
<tr><td class="author-text"> </td>
<td class="author-text">Six Apart, Ltd.</td></tr>
<tr><td class="author" align="right">Email: </td>
<td class="author-text"><a href="mailto:[email protected]">[email protected]</a></td></tr>
<tr cellpadding="3"><td> </td><td> </td></tr>
<tr><td class="author-text"> </td>
<td class="author-text">Joseph Smarr (editor)</td></tr>
<tr><td class="author-text"> </td>
<td class="author-text">Plaxo, Inc.</td></tr>
<tr><td class="author" align="right">Email: </td>
<td class="author-text"><a href="mailto:[email protected]">[email protected]</a></td></tr>
<tr cellpadding="3"><td> </td><td> </td></tr>
<tr><td class="author-text"> </td>
<td class="author-text">Allen Tom (editor)</td></tr>
<tr><td class="author-text"> </td>
<td class="author-text">Yahoo!, Inc.</td></tr>
<tr><td class="author" align="right">Email: </td>
<td class="author-text"><a href="mailto:[email protected]">[email protected]</a></td></tr>
</tbody></table>
</body></html>