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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html lang="en"><head><title>OpenID Authentication 1.1</title>
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<table summary="layout" class="bug" align="right" cellpadding="0" cellspacing="2"><tbody><tr><td class="bug"><a href="#toc" class="link2"> 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"> </td><td class="header">D. Recordon</td></tr>
<tr><td class="header"> </td><td class="header">B. Fitzpatrick</td></tr>
<tr><td class="header"> </td><td class="header">May 2006</td></tr>
</tbody></table></td></tr></tbody></table>
<div align="right"><span class="title"><br>OpenID Authentication 1.1</span></div>
<h3>Abstract</h3>
<p>OpenID Authenticaion provides a way to prove that an End User
owns an Identity URL. It does this without passing around their
password, email address, or anything they don't want it
to.
</p>
<p>OpenID is completely decentralized meaning that anyone
can choose to be a Consumer or Identity Provider without having
to register or be approved by any central authority. End User's
can pick which Identity Provider they wish to use and preserve
their Identity as they move between Providers.
</p>
<p>While nothing in the protocol requires JavaScript or modern
browsers, the authentication scheme plays nicely with
"AJAX"-style setups, so an End User can prove their Identity to
a Consumer without having to leave the page they are on.
</p>
<p>The OpenID Authentication specification does not provide any
mechanism to exchange profile information, though Consumers of
an Identity can learn more about an End User from any public,
semantically interesting documents linked thereunder (FOAF, RSS,
Atom, vCARD, etc.). Extensions are being built on top of the
foundation created by OpenID Authentication to provide
mechanisms to exchange profile information.
</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>
Overview<br>
<a href="#anchor4">3.1.</a>
Transforming a HTML Document Into an Identifier<br>
<a href="#delegating_authentication">3.1.1.</a>
Delegating Authentication<br>
<a href="#anchor6">3.2.</a>
Submitting a Claimed Identifier<br>
<a href="#anchor8">3.3.</a>
Consumer Site Fetches the Identifier URL<br>
<a href="#smart_vs_dumb">3.4.</a>
Smart vs Dumb Mode<br>
<a href="#anchor11">3.5.</a>
Consumer Verifies the Identifier<br>
<a href="#anchor12">4.</a>
Modes<br>
<a href="#mode_associate">4.1.</a>
associate<br>
<a href="#anchor13">4.1.1.</a>
Request Parameters<br>
<a href="#anchor14">4.1.2.</a>
Response Parameters<br>
<a href="#anchor15">4.1.3.</a>
Extra Notes<br>
<a href="#mode_checkid_immediate">4.2.</a>
checkid_immediate<br>
<a href="#anchor16">4.2.1.</a>
Request Parameters<br>
<a href="#anchor17">4.2.2.</a>
Response Parameters<br>
<a href="#anchor21">4.2.3.</a>
Extra Notes<br>
<a href="#mode_checkid_setup">4.3.</a>
checkid_setup<br>
<a href="#anchor22">4.3.1.</a>
Request Parameters<br>
<a href="#anchor23">4.3.2.</a>
Respone Parameters<br>
<a href="#anchor26">4.3.3.</a>
Extra Notes<br>
<a href="#mode_check_authentication">4.4.</a>
check_authentication<br>
<a href="#anchor27">4.4.1.</a>
Request Parameters<br>
<a href="#anchor28">4.4.2.</a>
Response Parameters<br>
<a href="#anchor29">4.4.3.</a>
Extra Notes<br>
<a href="#anchor30">5.</a>
Security Considerations<br>
<a href="#defaults">Appendix A.</a>
Default Values<br>
<a href="#pvalue">Appendix A.1.</a>
Diffie-Hellman P Value<br>
<a href="#anchor31">Appendix B.</a>
Error Responses<br>
<a href="#anchor32">Appendix C.</a>
Key-Value Format<br>
<a href="#limits">Appendix D.</a>
Limits<br>
<a href="#anchor33">Appendix E.</a>
Misc<br>
<a href="#rfc.references1">6.</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="bug" align="right" cellpadding="0" cellspacing="2"><tbody><tr><td class="bug"><a href="#toc" class="link2"> 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, B., “Key words for use in RFCs to Indicate Requirement Levels,” .</span><span>)</span></a>.
</p>
<a name="anchor2"></a><br><hr>
<table summary="layout" class="bug" align="right" cellpadding="0" cellspacing="2"><tbody><tr><td class="bug"><a href="#toc" class="link2"> TOC </a></td></tr></tbody></table>
<a name="rfc.section.2"></a><h3>2. Terminology</h3>
<p>
</p>
<blockquote class="text"><dl>
<dt>End User:</dt>
<dd>The actual human user who wants to
prove their Identity to a Consumer.
</dd>
<dt>Identifier:</dt>
<dd>An Identifier is just a URL. The whole
flow of the OpenID Authentication protocol is about proving
that an End User is, owns, a URL.
</dd>
<dt>Claimed Identifier:</dt>
<dd>An Identifier that the End
User says they own, though that has not yet been verified by
the Consumer.
</dd>
<dt>Verified Identifier:</dt>
<dd>An Identifier that the
End User has proven to a Consumer that they own.
</dd>
<dt>Consumer:</dt>
<dd>A web service that wants proof that
the End User owns the Claimed Identifier.
</dd>
<dt>Identity Provider:</dt>
<dd>Also called "IdP" or
"Server". This is the OpenID Authentication server
that a Consumer contacts for cryptographic proof that the
End User owns the Claimed Identifier.
<br>
How the End User authenticates to their Identity Provider is
outside of the scope of OpenID Authenticaiton.
</dd>
<dt>User-Agent:</dt>
<dd>The End User's web browser. No
special plug-ins or JavaScript required.
</dd>
</dl></blockquote><p>
</p>
<a name="anchor3"></a><br><hr>
<table summary="layout" class="bug" align="right" cellpadding="0" cellspacing="2"><tbody><tr><td class="bug"><a href="#toc" class="link2"> TOC </a></td></tr></tbody></table>
<a name="rfc.section.3"></a><h3>3. Overview</h3>
<a name="anchor4"></a><br><hr>
<table summary="layout" class="bug" align="right" cellpadding="0" cellspacing="2"><tbody><tr><td class="bug"><a href="#toc" class="link2"> TOC </a></td></tr></tbody></table>
<a name="rfc.section.3.1"></a><h3>3.1. Transforming a HTML Document Into an Identifier</h3>
<p>In order for a Consumer to know the Identity Provider
authoritative for an Identifier, the End User must add markup to
the HEAD section of the HTML document located at their
URL. The host of the HTML document is NOT REQUIRED to also be
the End User's Identity Provider; the Identifier URL and
Identity Provider can be fully decoupled services.
</p>
<p>To use http://example.com/ as the End User's Identifier
http://openid.example.com as their Identity Provider, the
following tag would be added to the HEAD section of the HTML
document returned when fetching their Identifier URL.
</p>
<p><link rel="openid.server"
href="http://openid.example.com/">
</p>
<a name="delegating_authentication"></a><br><hr>
<table summary="layout" class="bug" align="right" cellpadding="0" cellspacing="2"><tbody><tr><td class="bug"><a href="#toc" class="link2"> TOC </a></td></tr></tbody></table>
<a name="rfc.section.3.1.1"></a><h3>3.1.1. Delegating Authentication</h3>
<p>If the End User's host is not capable of running an
Identity Provider, or the End User wishes to use one running
on a different host, they will need to delegate their
authentication. For example, if they want to use their
website, http://www.example.com/, as their Identifier, but
don't have the means, or desire, to run an Identity
Provider.
</p>
<p>If they have a LiveJournal account (say, user
"exampleuser"), and know that LiveJournal provides an OpenID
Identity Provider and that it'll assert that they control
the Identifier http://exampleuser.livejournal.com/ they would
be able to delegate their authentication to LiveJournal's
Identity Provider..
</p>
<p>So, to use www.example.com as their Identifier, but have
Consumers actually verify
http://exampleuser.livejournal.com/ with the Identity
Provider located at
http://www.livejournal.com/openid/server.bml, they'd add the
following tags to the HEAD section of the HTML document
returned when fetching their Identifier URL.
</p>
<p><link rel="openid.server"
href="http://www.livejournal.com/openid/server.bml">
</p>
<p><link rel="openid.delegate"
href="http://exampleuser.livejournal.com/">
</p>
<p>Now, when a Consumer sees that, it'll talk to
http://www.livejournal.com/openid/server.bml and ask if
the End User is exampleuser.livejournal.com, never mentioning
www.example.com anywhere on the wire.
</p>
<p>The main advantage of this is that an End User can keep
their Identifier over many years, even as services come and
go; they'll just keep changing who they delegate to.
</p>
<a name="anchor5"></a><br><hr>
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<a name="rfc.section.3.1.2"></a><h3>3.1.2. Important Notes</h3>
<p>
</p>
<ul class="text">
<li>The declared openid.server URL MAY contain existing
query parameters and they MUST be properly preserved when
appending extra query parameters. For example, not adding
a second question mark if one already exists.
</li>
<li>The openid.server and openid.delegate URLs MUST
be absolute URLs. Consumers MUST NOT attempt to
resolve relative URLs.
</li>
<li>The openid.server and openid.delegate URLs MUST
NOT include entities other than &, <, >,
and ". Other characters that would not be
valid in the HTML document or that cannot be
represented in the document's character encoding
MUST be escaped using the %xx mechanism as described
in <a class="info" href="#RFC2396">[RFC2396]<span> (</span><span class="info">Berners-Lee, T., “Uniform Resource Identifiers (URI): Generic Syntax,” .</span><span>)</span></a>.
</li>
</ul><p>
</p>
<a name="anchor6"></a><br><hr>
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<a name="rfc.section.3.2"></a><h3>3.2. Submitting a Claimed Identifier</h3>
<p>Continuing this example, the End User visits a Consumer
site which supports OpenID Authentication. The Consumer
presents the End User with a form field for them to enter
their Identifier URL.
</p>
<p>
</p><p>For Example:
</p><pre> ----------------------------------
|[logo]example.com | [Login Button]
----------------------------------
</pre>
<a name="anchor7"></a><br><hr>
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<a name="rfc.section.3.2.1"></a><h3>3.2.1. Important Notes</h3>
<p>
</p>
<ul class="text">
<li>It is RECOMMENDED that every Consumer place the
<a href="http://openid.net/login-bg.gif">OpenID
logo</a> at the beginning of the form field where the
End User enters their Identifier URL.
</li>
<li>The End User is NOT REQUIRED to prefix
their Identifier URL with "http://" or postfix it with a
trailing slash. Consumers MUST canonicalize the Identifier
URL, following redirects, and note the final URL.
The final, canonicalized URL is the End User's
Identifier.
</li>
<li>It is RECOMMENDED that the form field be named
"openid_url" so User-Agent's will auto-complete the End
User's Identifier URL in the same way the eCommerce world
tends to use conventions like "address1" and
"address2".
</li>
</ul><p>
</p>
<a name="anchor8"></a><br><hr>
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<a name="rfc.section.3.3"></a><h3>3.3. Consumer Site Fetches the Identifier URL</h3>
<p>Now the Consumer site fetchs the document located at the End
User's Claimed Identifier. The Consumer then parses the HEAD
section for the "openid.server" and the optional
"openid.delegate" declarations.
</p>
<a name="anchor9"></a><br><hr>
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<a name="rfc.section.3.3.1"></a><h3>3.3.1. Important Notes</h3>
<p>
</p>
<ul class="text">
<li>The End User could be malicious and try to make the
Consumer connect to an internal network, tarpit, etc. It
is RECOMMENDED that Consumers use a paranoid HTTP library like <a href="http://search.cpan.org/%7Ebradfitz/LWPx-ParanoidAgent-1.02/lib/LWPx/ParanoidAgent.pm">LWPx::ParanoidAgent</a> that protects against these sorts of attacks.
</li>
<li>Consumers MUST implement support for <a class="info" href="#delegating_authentication">Delegation<span> (</span><span class="info">Delegating Authentication</span><span>)</span></a>.
</li>
</ul><p>
</p>
<a name="smart_vs_dumb"></a><br><hr>
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<a name="rfc.section.3.4"></a><h3>3.4. Smart vs Dumb Mode</h3>
<p>OpenID Authentication supports both a "smart mode" and
"dumb mode" to accomodate Consumers of differing
capabilities. A smart Consumer does a little more work at the
beginning to save itself work later, but requires local
caching of state information. A dumb Consumer is completely
stateless, but requires extra an HTTP request.
</p>
<a name="anchor10"></a><br><hr>
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<a name="rfc.section.3.4.1"></a><h3>3.4.1. Important Notes for Smart Mode</h3>
<p>
</p>
<ul class="text">
<li>It's RECOMMENDED that a Consumer first submit an
<a class="info" href="#mode_associate">associate request<span> (</span><span class="info">associate</span><span>)</span></a>
to the End User's Identity Provider and request a shared
secret if the Consumer does not already have one
cached. This shared secret SHOULD be used as the
HMAC-SHA1 key in future identity check requests until it
expires.
</li>
<li>The shared secret can be exchanged either in
plain-text or encrypted with a Diffie-Hellman-negotiated
secret. Note that if Diffie-Hellman is used, it's only
used in the associate mode. The <a class="info" href="#mode_checkid_immediate">checkid_immediate<span> (</span><span class="info">checkid_immediate</span><span>)</span></a>
and <a class="info" href="#mode_checkid_setup">checkid_setup<span> (</span><span class="info">checkid_setup</span><span>)</span></a>
modes assume the Consumer already has a shared secret,
regardless of how it got it.
</li>
</ul><p>
</p>
<a name="anchor11"></a><br><hr>
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<a name="rfc.section.3.5"></a><h3>3.5. Consumer Verifies the Identifier</h3>
<p>The Consumer now constructs a URL to the Identity
Provider's <a class="info" href="#mode_checkid_immediate">checkid_immediate<span> (</span><span class="info">checkid_immediate</span><span>)</span></a> (or
<a class="info" href="#mode_checkid_setup">checkid_setup<span> (</span><span class="info">checkid_setup</span><span>)</span></a>) URLs
and sends the User-Agent to it.
</p>
<p>By sending the User-Agent there, the End User's cookies and
whatever other login credentials are sent back to their
trusted Identity Provider. The Identity Provider does its
work, appends its response onto the supplied openid.return_to
URL, and sends the User-Agent back to the Consumer.
</p>
<a name="anchor12"></a><br><hr>
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<a name="rfc.section.4"></a><h3>4. Modes</h3>
<a name="mode_associate"></a><br><hr>
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<a name="rfc.section.4.1"></a><h3>4.1. associate</h3>
<p>
</p>
<ul class="text">
<li>Description: Establish a shared secret between Consumer
and Identity Provider.
</li>
<li>HTTP method: POST
</li>
<li>Flow: Consumer -> IdP -> Consumer
</li>
</ul><p>
</p>
<a name="anchor13"></a><br><hr>
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<a name="rfc.section.4.1.1"></a><h3>4.1.1. Request Parameters</h3>
<p>
</p>
<ul class="text">
<li>
openid.mode
<blockquote class="text">
<p>Value: "associate"
</p>
</blockquote>
</li>
<li>
openid.assoc_type
<blockquote class="text">
<p>Value: Preferred association type
</p>
<p>Default: "HMAC-SHA1"
</p>
<p>Note: Optional; Currently only one value.
</p>
</blockquote>
</li>
<li>
openid.session_type
<blockquote class="text">
<p>Value: Blank or "DH-SHA1"
</p>
<p>Default: Blank. (cleartext)
</p>
<p>Note: It is RECOMMENDED that DH-SHA1 mode is used
to encrypt the shared secret.
</p>
</blockquote>
</li>
<li>
openid.dh_modulus
<blockquote class="text">
<p>Value: base64(btwoc(p))
</p>
<p>Note: See <a class="info" href="#pvalue">Appendix A.1<span> (</span><span class="info">Diffie-Hellman P Value</span><span>)</span></a> for default p value.
</p>
</blockquote>
</li>
<li>
openid.dh_gen
<blockquote class="text">
<p>Value: base64(btwoc(g))
</p>
<p>Default: g = 2
</p>
<p>Note: Only if using DH-SHA1 session_type. Should
be specified if openid.dh_modulus is specified.
</p>
</blockquote>
</li>
<li>
openid.dh_consumer_public
<blockquote class="text">
<p>Value: base64(btwoc(g ^ x mod p))
</p>
<p>Note: REQUIRED if using DH-SHA1 session_type.
</p>
</blockquote>
</li>
</ul><p>
</p>
<a name="anchor14"></a><br><hr>
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<a name="rfc.section.4.1.2"></a><h3>4.1.2. Response Parameters</h3>
<p>Response format: Key-Value Pairs
</p>
<p>
</p>
<ul class="text">
<li>
assoc_type
<blockquote class="text">
<p>Value: The association type for the returned handle.
</p>
<p>Note: The only current mode is HMAC-SHA1, and all
Consumers MUST support it. When caching, the
Consumer MUST map an assoc_handle to both its secret
and its assoc_type.
</p>
</blockquote>
</li>
<li>
assoc_handle
<blockquote class="text">
<p>Value: The association handle to be provided in future
transactions.
</p>
<p>Note: Consumers MUST NOT reuse this association
handle after the corresponding expires_in value.
</p>
</blockquote>
</li>
<li>
expires_in
<blockquote class="text">
<p>Value: The number of seconds this association
handle is good for in base10 ASCII.
</p>
</blockquote>
</li>
<li>
session_type
<blockquote class="text">
<p>Value: The encryption mode that the Provider chose. MAY be
blank, absent, or "DH-SHA1".
</p>
</blockquote>
</li>
<li>
dh_server_public
<blockquote class="text">
<p>Value: base64(btwoc(g ^ y mod p))
</p>
<p>Description: The Provider's <a class="info" href="#RFC2631">Diffie-Hellman public key<span> (</span><span class="info">Rescorla, E., “Diffie-Hellman Key Agreement Method,” .</span><span>)</span></a> [RFC2631], if
using DH-SHA1.
</p>
</blockquote>
</li>
<li>
enc_mac_key
<blockquote class="text">
<p>Value: base64(SHA1(btwoc(g ^ (xy) mod p)) XOR secret(assoc_handle))
</p>
<p>Description: The encrypted shared secret, if using
DH-SHA1.
</p>
</blockquote>
</li>
<li>
mac_key
<blockquote class="text">
<p>Value: base64(secret(assoc_handle))
</p>
<p>Description: The plaintext shared secret, if not
using DH-SHA1.
</p>
</blockquote>
</li>
</ul><p>
</p>
<a name="anchor15"></a><br><hr>
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<a name="rfc.section.4.1.3"></a><h3>4.1.3. Extra Notes</h3>
<p>
</p>
<ul class="text">
<li>A Consumer can ask a server for DH-SHA1 encryption and
get back a plaintext secret. If this troubles you, don't
use the handle and instead use dumb mode with that
Identity Provider.
<br>
<br>
If somebody sniffed the plaintext secret, it won't
matter, since you'll never accept queries using that
association handle. If the Identity Provider can't do
DH-SHA1, it's probably limited in some way, but using
dumb mode is still safe, if not a little slower.
</li>
<li>If the Identity Provider chooses the server private
key 1 <= y < p-1. The shared DH-SHA1 secret is
thus g ^ xy mod p = (g ^ x) ^ y mod p = (g ^ y) ^ x mod
p. For more information, read the <a href="http://search.cpan.org/%7Ebtrott/Crypt-DH-0.06/lib/Crypt/DH.pm">Crypt::DH docs.</a>
</li>
<li>The underlying mac_key MUST be the same length as the
output of H, the hash function - in this instance, 160
bits (20 bytes) for DH-SHA1.
</li>
<li>If the Provider does not support DH-SHA1, they WILL ignore
the DH-SHA1 fields in the request and reply exactly as to a
non-DH-SHA1 request.
</li>
<li>When using DH-SHA1, the resulting key SHOULD be treated
as a binary string.
</li>
<li>Most integers are represented in big-endian signed two's
complement, Base64 encoded. In other words, btwoc is a
function that takes a bigint and returns its shortest
big-endian two's complement notation
</li>
</ul><p>
</p>
<a name="mode_checkid_immediate"></a><br><hr>
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<a name="rfc.section.4.2"></a><h3>4.2. checkid_immediate</h3>
<p>
</p>
<ul class="text">
<li>Description: Ask an Identity Provider if a End User owns the
Claimed Identifier, getting back an immediate "yes" or "can't say"
answer.
</li>
<li>HTTP method: GET
</li>
<li>Flow: Consumer -> User-Agent -> IdP -> User-Agent ->
Consumer
</li>
</ul><p>
</p>
<a name="anchor16"></a><br><hr>
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<a name="rfc.section.4.2.1"></a><h3>4.2.1. Request Parameters</h3>
<p>
</p>
<ul class="text">
<li>
openid.mode
<blockquote class="text">
<p>Value: "checkid_immediate"
</p>
</blockquote>
</li>
<li>
openid.identity
<blockquote class="text">
<p>Value: Claimed Identifier
</p>
</blockquote>
</li>
<li>
openid.assoc_handle
<blockquote class="text">
<p>Value: The assoc_handle from the associate request.
</p>
<p>Note: Optional; Consumer MUST use
check_authentication if an association handle isn't
provided or the Identity Provider feels it is invalid.
</p>
</blockquote>
</li>
<li>
openid.return_to
<blockquote class="text">
<p>Value: URL where the Provider SHOULD return the
User-Agent back to.
</p>
</blockquote>
</li>
<li>
openid.trust_root
<blockquote class="text">
<p>Value: URL the Provider SHALL ask the End User to trust.
</p>
<p>Default: return_to URL
</p>
<p>Optional; the URL which the End User SHALL
actually see to approve.
</p>
</blockquote>
</li>
</ul><p>
</p>
<a name="anchor17"></a><br><hr>
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<a name="rfc.section.4.2.2"></a><h3>4.2.2. Response Parameters</h3>
<p>Response format: query string arguments
</p>
<a name="anchor18"></a><br><hr>
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<a name="rfc.section.4.2.2.1"></a><h3>4.2.2.1. Always Sent</h3>
<p>
</p>
<ul class="text">
<li>
openid.mode
<blockquote class="text">
<p>Value: "id_res"
</p>
</blockquote>
</li>
</ul><p>
</p>
<a name="anchor19"></a><br><hr>
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<a name="rfc.section.4.2.2.2"></a><h3>4.2.2.2. Sent on Failed Assertion</h3>
<p>
</p>
<ul class="text">
<li>
openid.user_setup_url
<blockquote class="text">
<p>Value: URL to redirect User-Agent to so the End
User can do whatever's necessary to fulfill the
assertion.
</p>
</blockquote>
</li>
</ul><p>
</p>
<a name="anchor20"></a><br><hr>
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<a name="rfc.section.4.2.2.3"></a><h3>4.2.2.3. Sent on Positive Assertion</h3>
<p>
</p>
<ul class="text">
<li>
openid.identity
<blockquote class="text">
<p>Value: Verified Identifier
</p>
</blockquote>
</li>
<li>
openid.assoc_handle
<blockquote class="text">
<p>Value: Opaque association handle being used to
find the HMAC key for the signature.
</p>
</blockquote>
</li>
<li>
openid.return_to
<blockquote class="text">
<p>Value: Verbatim copy of the return_to URL
parameter sent in the request, before the Provider
modified it.
</p>
</blockquote>
</li>
<li>
openid.signed
<blockquote class="text">
<p>Value: Comma-seperated list of signed fields.
</p>
<p>Note: Fields without the "openid." prefix that
the signature covers. For example,
"mode,identity,return_to".
</p>
</blockquote>
</li>
<li>
openid.sig
<blockquote class="text">
<p>Value: base64(HMAC(secret(assoc_handle), token_contents)
</p>
<p>Note: Where token_contents is a key-value
format string of all the signed keys and values in
this response. They MUST be in the same order as
listed in the openid.signed field. Consumer SHALL
recreate the token_contents string prior to
checking the signature. See <a class="info" href="#limits">Appendix D<span> (</span><span class="info">Limits</span><span>)</span></a>.
</p>
</blockquote>
</li>
<li>
openid.invalidate_handle
<blockquote class="text">
<p>Value: Optional; The association handle sent in
the request if the Provider did not accept or
recognize it.
</p>
</blockquote>
</li>
</ul><p>
</p>
<a name="anchor21"></a><br><hr>
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<a name="rfc.section.4.2.3"></a><h3>4.2.3. Extra Notes</h3>
<p>
</p>
<ul class="text">
<li>This mode is commonly used for "AJAX"-style
setups. The more classic mode to check a Claimed
Identifier is <a class="info" href="#mode_checkid_setup">checkid_setup<span> (</span><span class="info">checkid_setup</span><span>)</span></a>.
</li>
<li>An Identity Provider SHOULD only assert URLs that it
manages/produces directly. If a End User wants to assert
other URLs outside of that Identity Provider's realm,
they MUST use <a class="info" href="#delegating_authentication">delegation<span> (</span><span class="info">Delegating Authentication</span><span>)</span></a>.
</li>
<li>The openid.return_to URL provided MAY contain an
existing query string, and the Provider MUST preserve it
when appending the response parameters. OpenID Consumer's
SHOULD add a self-signed nonce with
Consumer-local timestamp in the openid.return_to URL
parameters to prevent replay attacks. Details of that
are left up to the Consumer.
<br>
<br>
However, because the openid.return_to URL is signed by
the Idenity Provide, a Consumer can make sure outside
parties haven't sent id_res responses with mismatching
openid.return_to URLs and signatures.
</li>
<li>If the Identity Provider didn't accept/recognize the
provided assoc_handle for whatever reason, it'll choose
its own to use, and copy the one provided back into
openid.invalidate_handle, to tell the Consumer to stop
using it. The Consumer SHOULD then send it along in a
<a class="info" href="#mode_check_authentication">check_authentication<span> (</span><span class="info">check_authentication</span><span>)</span></a>
request to verify it actually is no longer valid.
</li>
<li>If the Identifier assertion fails, the Identity
Provider provides the openid.user_setup_url for where
the End User can do whatever's necessary to fulfill the
assertion, be it login, setup permissions, etc. The
server SHOULD return a URL which doesn't imply anything