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<?xml version="1.0" encoding="utf-8"?>
<html xmlns="http://www.w3.org/1999/xhtml"
xmlns:info="http://planete-kraus.eu/ns/info"
xml:lang="en">
<head>
<link rel="stylesheet" type="text/css" href="style.css"/>
<title>Webid-oidc manual</title>
<info:subtitle>for version <info:version />,
<info:updated /></info:subtitle>
<info:copying>
<p>
This is the manual of webid-oidc (version <info:version />,
<info:updated />), an implementation of the Solid
authentication protocol for guile, client and server.
</p>
<p>Copyright <info:copyright-symbol /> 2020, 2021 Vivien
Kraus</p>
<info:quotation>
<p>
Permission is granted to copy, distribute and/or modify this
document under the terms of the GNU Free Documentation
License, Version 1.3 or any later version published by the
Free Software Foundation; with no Invariant Sections, with no
Front-Cover Texts, and with no Back-Cover Texts. A copy of the
license is included in the section entitled ``GNU Free
Documentation License''
</p>
</info:quotation>
</info:copying>
<info:author>
<a href="mailto:vivien@planete-kraus.eu">Vivien Kraus</a>
</info:author>
<info:dircategory>
Software libraries
</info:dircategory>
<info:direntry>
<info:direntry-entry name="webid-oidc">
Decentralized Authentication on the Web.
</info:direntry-entry>
</info:direntry>
</head>
<body>
<h1>Decentralized Authentication on the Web</h1>
<p>
Authentication on the web is currently handled in the following
way: anyone can install a server that will authenticate users on
the web. The problem is interoperability. If a client (an
application) wants to authenticate a user, it has to be approved
by the authentication server. In other words, if
<info:var>useful-program</info:var> wants to authenticate
<info:var>MegaCorp</info:var> users, then
<info:var>useful-program</info:var> has to register to
<info:var>MegaCorp</info:var> first, and get approved. This goes
against the principle of permission-less innovation, which is at
the heart of the web.
</p>
<p>
In the decentralized authentication web, the best attempt so far
is that of ActivityPub. All servers are interoperable with
respect to authentication: if user A emits an activity, it is
forwarded by A's server to its recipients, and A's server is
responsible for A's identity.
</p>
<p>
The problem with that approach is that the data is tied to the
application. It is not possible to use another application to
process the data differently, or to use multiple data sources,
in an interoperable way (without the ActivityPub server
knowing). This means that on Activitypub, microblogging
applications will not present different activities
correctly. This also means that it is difficult to write a free
replacement to a non-free application program, because it would
need to manage the data.
</p>
<p>
In the Solid ecosystem, there is a clear distinction between
servers and applications. An application is free to read data
from all places at the same time, using a permission-less
authentication system. Since the applications do not need to
store data, the cost of having users is neglectible, so users do
not need prior approval before using them (making captchas and
the like a thing of the past). Servers do not have a say in
which applications the user uses.
</p>
<p>
The authentication used is a slight modification of the
well-established OpenID Connect. It is intended to work in a web
browser, but this package demonstrates that it also works
without a web browser.
</p>
<h1>The Json Web Token</h1>
<p>
The Json Web Token, or <info:dfn>JWT</info:dfn>, is a terse
representation of a pair of JSON objects: the
<info:dfn>header</info:dfn>, and the
<info:dfn>payload</info:dfn>. The JWT can be
<info:dfn>encoded</info:dfn> as a Json Web Signature
(<info:dfn>JWS</info:dfn>), in which case the header is encoded
to base64 with the URL alphabet, and without padding characters,
the payload is also encoded to base64, and the concatenation of
the encoding of the header, a dot, and the encoding of the
payload is signed with some cryptography algorithm. In the
following, we will only be interested by public-key
cryptography. The concatenation of header, dot, payload, dot and
signature in base64 is the encoding of the JWT.
</p>
<p>
Decoded JWT are represented as a pair. The car of the pair is
the header, and the cdr is the payload. Both the header and the
payload use the JSON representation from srfi-180: objects are
alists of <strong>symbols</strong> to values, arrays are
vectors. It is unfortunate that guile-json has a slightly
different representation, where alist keys are
<emph>strings</emph>, but we hope that in the future SRFI-180
will be more closely respected.
</p>
<h2>The ID token</h2>
<p>
The ID token is a special JWT that the application keeps for
itself. It is signed by the identity provider, and contains the
following claims:
</p>
<ul>
<li><emph>webid</emph>, the URI of the user’s webid;</li>
<li><emph>iss</emph>, the URI of the identity provider (issuer);</li>
<li><emph>sub</emph>, the username (the webid-oidc issuer puts the webid again here, but it could be any string);</li>
<li><emph>aud</emph>, the ID of the client application that is intended to receive the ID token;</li>
<li><emph>nonce</emph>, some random data to change the signature;</li>
<li><emph>exp</emph>, an UTC time (in seconds) for when the token expires;</li>
<li><emph>iat</emph>, the time when it was issued.</li>
</ul>
<p>
There are functions to work with ID tokens
in <emph>(webid-oidc oidc-id-token)</emph>.
</p>
<info:deffn type="function" name="id-token?" arguments="object">
<p>
Check that <info:var>object</info:var> is a decoded ID token.
</p>
</info:deffn>
<p>
The following helper functions convert URIs to the URIs
from <emph>(web uri)</emph> and times
to <emph>(srfi srfi-19)</emph> dates.
</p>
<info:deffn type="function" name="id-token-webid" arguments="token">
<info:deffnx type="function" name="id-token-iss" arguments="token" />
<info:deffnx type="function" name="id-token-sub" arguments="token" />
<info:deffnx type="function" name="id-token-aud" arguments="token" />
<info:deffnx type="function" name="id-token-nonce" arguments="token" />
<info:deffnx type="function" name="id-token-exp" arguments="token" />
<info:deffnx type="function" name="id-token-iat" arguments="token" />
<p>
Get the suitable field from the payload
of <info:var>token</info:var>.
</p>
</info:deffn>
<p>
ID tokens can be signed and encoded as a string, or decoded.
</p>
<info:deffn type="function" name="id-token-decode" arguments="token [#http-get]">
<p>
Decode <info:var>token</info:var>, as a string, into a decoded
token. The signature verification will need to fetch the oidc
configuration of the claimed issuer, and check the signature
against the published keys. The <pre>http-get</pre> optional
keyword argument can set a different implementation
of <pre>http-get</pre>
from <emph>(web client)</emph>. Return <pre>#f</pre> if
it failed, or the decoded token otherwise.
</p>
</info:deffn>
<info:deffn type="function" name="id-token-encode" arguments="token key">
<p>
Encode <info:var>token</info:var> and sign it with the
issuer’s <info:var>key</info:var>.
</p>
</info:deffn>
<info:deffn type="function" name="issue-id-token" arguments="issuer-key #alg #webid #iss #sub #aud #exp #iat">
<p>
Create an ID token, and encode it with
<info:var>issuer-key</info:var>.
</p>
</info:deffn>
<h2>The access token</h2>
<p>
The access token is obtained by the client through a token
request, and is presented to the server on each authenticated
request. It is signed by the identity provider, and it contains
enough information so that the server knows who the user is and
who the agent is, and most importantly the fingerprint of the
key that the client should use in a DPoP proof.
</p>
<p>
The API is defined in
<emph>(webid-oidc access-token)</emph>.
</p>
<info:deffn type="function" name="access-token?" arguments="object">
<p>
Check that <info:var>object</info:var> is a decoded access token.
</p>
</info:deffn>
<p>
There are field getters for the access token:
</p>
<info:deffn type="function" name="access-token-webid" arguments="token">
<info:deffnx type="function" name="access-token-iss" arguments="token" />
<info:deffnx type="function" name="access-token-aud" arguments="token" />
<info:deffnx type="function" name="access-token-exp" arguments="token" />
<info:deffnx type="function" name="access-token-iat" arguments="token" />
<info:deffnx type="function" name="access-token-cnf/jkt" arguments="token" />
<info:deffnx type="function" name="access-token-client-id" arguments="token" />
<p>
Get the suitable field from the payload
of <info:var>token</info:var>.
</p>
</info:deffn>
<p>
Access tokens can be signed and encoded as a string, or decoded.
</p>
<info:deffn type="function" name="access-token-decode" arguments="token [#http-get]">
<p>
Decode <info:var>token</info:var>, as a string, into a decoded
token. As with the ID token, the signature verification will
need to fetch the oidc configuration of the claimed issuer,
and check the signature against the published keys. The
<pre>http-get</pre> optional keyword argument can set a
different implementation of <pre>http-get</pre> from
<emph>(web client)</emph>, for instance to re-use the
what has been obtained by the ID token validation. Return
<pre>#f</pre> if it failed, or the decoded token otherwise.
</p>
</info:deffn>
<info:deffn type="function" name="access-token-encode" arguments="token key">
<p>
Encode <info:var>token</info:var> and sign it with the
issuer’s <info:var>key</info:var>.
</p>
</info:deffn>
<info:deffn type="function" name="issue-access-token" arguments="issuer-key #alg #webid #iss #exp #iat [#client-key | #cnf/jkt] #client-id ">
<p>
Create an access token, and encode it with
<info:var>issuer-key</info:var>. You can either set the
<pre>#:cnf/jkt</pre> keyword argument with the fingerprint of
the client key, or set <pre>#:client-key</pre> directly, in
which case the fingerprint will be computed for you.
</p>
</info:deffn>
<h2>The DPoP proof</h2>
<p>
This is a special JWT, that is signed by a key controlled by the
application. The access token certifies that the key used to
sign the proof is approved by the identity provider.
</p>
<info:deffn type="function" name="dpop-proof?" arguments="proof">
<p>
Check that the <info:var>proof</info:var> is a decoded DPoP
proof. The validity of the proof is not checked by this
function.
</p>
</info:deffn>
<info:deffn type="function" name="dpop-proof-alg" arguments="proof">
<info:deffnx type="function" name="dpop-proof-jwk" arguments="proof" />
<info:deffnx type="function" name="dpop-proof-jti" arguments="proof" />
<info:deffnx type="function" name="dpop-proof-htm" arguments="proof" />
<info:deffnx type="function" name="dpop-proof-htu" arguments="proof" />
<info:deffnx type="function" name="dpop-proof-iat" arguments="proof" />
<p>
Get the corresponding field of the proof.
</p>
</info:deffn>
<info:deffn type="function" name="dpop-proof-decode" arguments="current-time jti-list method uri str cnf/check">
<p>
Check and decode a DPoP proof encoded
as <info:var>str</info:var>.
</p>
<p>
The <info:var>current-time</info:var> is passed as a date,
time or number (of seconds).
</p>
<p>
In order to prevent replay attacks, each proof has a unique
random string that is remembered
in <info:var>jti-list</info:var> until its expiration date is
reached. See the <pre>make-jti-list</pre> function.
</p>
<p>
The proof is limited to the scope of
one <info:var>uri</info:var> and
one <info:var>method</info:var>
(<pre>'GET</pre>, <pre>'POST</pre> and so on).
</p>
<p>
Finally, the key that is used to sign the proof should be
confirmed by the identity provider. To this end,
the <info:var>cnf/check</info:var> function is called with the
fingerprint of the key. The function should check that the
fingerprint is OK (return a boolean).
</p>
</info:deffn>
<info:deffn type="function"
name="make-jti-list"
arguments="">
<p>
This function in <emph>(webid-oidc jti-list)</emph>
creates an in-memory, async-safe, thread-safe cache for the
proof IDs.
</p>
</info:deffn>
<info:deffn type="function" name="dpop-proof-encode" arguments="proof key">
<p>
Encode the proof and sign it with <info:var>key</info:var>. To
generate valid proofs, <info:var>key</info:var> should be the
private key corresponding to the <pre>jwk</pre> field of the
proof.
</p>
</info:deffn>
<info:deffn type="function" name="issue-dpop-proof" arguments="client-key #alg #htm #htu #iat">
<p>
Create a proof, sign it and encode it with
<info:var>client-key</info:var>. <info:var>client-key</info:var>
should contain both the private and public key, because the
public part is written in the proof and the private part is
used to sign it.
</p>
</info:deffn>
<h2>Generic JWTs</h2>
<p>
You can parse generic JWTs signed with JWS with the following
functions from <emph>(webid-oidc jws)</emph>.
</p>
<info:deffn type="function" name="jws?" arguments="jwt">
<p>
Check that <info:var>jwt</info:var> is a decoded JWT signed
with JWS.
</p>
</info:deffn>
<info:deffn type="function" name="jws-alg" arguments="jwt">
<p>
Get the algorithm used to sign <info:var>jwt</info:var>.
</p>
</info:deffn>
<info:deffn type="function" name="jws-decode" arguments="str lookup-keys">
<p>
Check and decode a JWT signed with JWS and encoded
as <info:var>str</info:var>.
</p>
<p>
Since the decoding and signature verification happen at the
same time (for user friendliness), the
<info:var>lookup-keys</info:var> function is used. It is
passed as arguments the decoded JWT (but the signature is not
checked yet), and it should return a public key, a public key
set or a list of public keys. If the key lookup failed, this
function should raise an exception.
</p>
</info:deffn>
<info:deffn type="function" name="jws-encode" arguments="jwt key">
<p>
Encode the JWT and sign it with <info:var>key</info:var>.
</p>
</info:deffn>
<h1>Caching on server side</h1>
<p>
Both the identity provider and the resource server need to cache
things. The identity provider will cache application webids, and
the resource server will cache the identity provider keys, for
instance.
</p>
<p>
The solution is to use a file-system cache. Every response
(except those that have a cache-control policy of no-store) are
stored to a sub-directory of <emph>XDG_CACHE_HOME</emph>. Each
store has a 5% chance of triggering a cleanup of the cache. When
a cleanup occurs, each cached response has a 5% chance of being
dropped, including responses that are indicated as valid. This
way, a malicious cache response that has a maliciously long
validity will not stay too long in the cache. A log line will
indicate which items are dropped.
</p>
<p>
The <emph>(webid-oidc cache)</emph> module exports two
functions to deal with the cache.
</p>
<info:deffn type="function" name="clean-cache" arguments="[#percents] [#dir]">
<p>
Drop <info:var>percents</info:var>% of the cache right now, in
<info:var>dir</info:var> (defaults to some place within
<emph>XDG_CACHE_HOME</emph>).
</p>
</info:deffn>
<info:deffn type="function" name="with-cache" arguments="[#current-time] [#http-get] [#dir]">
<p>
Return a function acting as <emph>http-get</emph> from
<emph>(web client)</emph> (takes an URI as the first
parameter, and an optional <info:var>#:headers</info:var> set,
and returns 2 values, the response and its body).
</p>
<p>
The cache will be read and written in <info:var>dir</info:var>
(defaults to some place within <emph>XDG_CACHE_HOME</emph>),
and the <info:var>current-time</info:var> number of seconds,
SRFI-19 time or date, or time-returning thunk will be used to
check for the validity of responses.
</p>
<p>
The back-end function, <info:var>http-get</info:var>, defaults
to that of <emph>(web client)</emph>.
</p>
</info:deffn>
<h1>What if something goes wrong?</h1>
<p>
The library will raise an exception whenever something fishy
occurs. For instance, if a signature is invalid, or the
expiration date has passed. All exception types are defined in
<emph>(webid-oidc errors)</emph>.
</p>
<info:deffn type="function" name="error->str" arguments="error [#depth]">
<p>
Return a string explaining the <info:var>error</info:var>. You
can limit the <info:var>depth</info:var> of the explanation as
an integer.
</p>
</info:deffn>
<info:deftp type="exception type" name="&not-base64" arguments="value cause">
<p>
This exception is raised when the base64 decoding function
failed. <info:var>value</info:var> is the incorrect input,
and <info:var>cause</info:var> is a low-level error.
</p>
</info:deftp>
<info:deftp type="exception type" name="&not-json" arguments="value cause">
<p>
Cannot decode <info:var>value</info:var> to a JSON object.
</p>
</info:deftp>
<info:deftp type="exception type" name="&not-turtle" arguments="value cause">
<p>
Cannot decode <info:var>value</info:var> to a RDF graph.
</p>
</info:deftp>
<info:deftp type="exception type" name="&unsupported-crv" arguments="crv">
<p>
The identifier <info:var>crv</info:var> does not identify an
elliptic curve.
</p>
</info:deftp>
<info:deftp type="exception type" name="&not-a-jwk" arguments="value cause">
<p>
<info:var>value</info:var> does not identify a JWK.
</p>
</info:deftp>
<info:deftp type="exception type" name="&not-a-public-jwk" arguments="value cause">
<p>
<info:var>value</info:var> does not identify a public JWK.
</p>
</info:deftp>
<info:deftp type="exception type" name="&not-a-private-jwk" arguments="value cause">
<p>
<info:var>value</info:var> does not identify a private JWK.
</p>
</info:deftp>
<info:deftp type="exception type" name="&not-a-jwks" arguments="value cause">
<p>
<info:var>value</info:var> does not identify a set of public keys.
</p>
</info:deftp>
<info:deftp type="exception type" name="&unsupported-alg" arguments="value">
<p>
<info:var>value</info:var> does not identify a valid hash algorithm.
</p>
</info:deftp>
<info:deftp type="exception type" name="&invalid-signature" arguments="key payload signature">
<p>
<info:var>key</info:var> has not signed
<info:var>payload</info:var> with
<info:var>signature</info:var>.
</p>
</info:deftp>
<info:deftp type="exception type" name="&missing-alist-key" arguments="value key">
<p>
<info:var>value</info:var> isn’t an alist, or is missing a
value with <info:var>key</info:var>.
</p>
</info:deftp>
<info:deftp type="exception type" name="&not-a-jws-header" arguments="value cause">
<p>
<info:var>value</info:var> does not identify a decoded JWS header.
</p>
</info:deftp>
<info:deftp type="exception type" name="&not-a-jws-payload" arguments="value cause">
<p>
<info:var>value</info:var> does not identify a decoded JWS payload.
</p>
</info:deftp>
<info:deftp type="exception type" name="&not-a-jws" arguments="value cause">
<p>
<info:var>value</info:var> does not identify a decoded JWS.
</p>
</info:deftp>
<info:deftp type="exception type" name="&not-in-3-parts" arguments="string separator">
<p>
<info:var>string</info:var> cannot be split into 3 parts with
<info:var>separator</info:var>.
</p>
</info:deftp>
<info:deftp type="exception type" name="&no-matching-key" arguments="candidates alg payload signature">
<p>
No key among <info:var>candidates</info:var> could verify
<info:var>signature</info:var> signed with
<info:var>alg</info:var> for <info:var>payload</info:var>,
because the signature mismatched for all keys.
</p>
</info:deftp>
<info:deftp type="exception type" name="&cannot-decode-jws" arguments="value cause">
<p>
The <info:var>value</info:var> string is not an encoding of a valid JWS.
</p>
</info:deftp>
<info:deftp type="exception type" name="&cannot-encode-jws" arguments="jws key cause">
<p>
The <info:var>jws</info:var> cannot be signed.
</p>
</info:deftp>
<info:deftp type="exception type" name="&request-failed-unexpectedly" arguments="response-code response-reason-phrase">
<p>
We expected the request to succeed, but the server sent a
non-OK <info:var>response-code</info:var>.
</p>
</info:deftp>
<info:deftp type="exception type" name="&unexpected-header-value" arguments="header value">
<p>
We did not expect the server to respond with
<info:var>header</info:var> set to <info:var>value</info:var>.
</p>
</info:deftp>
<info:deftp type="exception type" name="&unexpected-response" arguments="response cause">
<p>
The <info:var>response</info:var> (from
<emph>(web response)</emph>) is not appropriate.
</p>
</info:deftp>
<info:deftp type="exception type" name="&not-an-oidc-configuration" arguments="value cause">
<p>
The <info:var>value</info:var> is not an OIDC configuration.
</p>
</info:deftp>
<info:deftp type="exception type" name="&incorrect-webid-field" arguments="value">
<p>
The <info:var>value</info:var> of the webid field in the JWT
is missing (if <pre>#f</pre>), or not an acceptable value.
</p>
</info:deftp>
<info:deftp type="exception type" name="&incorrect-sub-field" arguments="value">
<p>
The <info:var>value</info:var> of the sub field is incorrect.
</p>
</info:deftp>
<info:deftp type="exception type" name="&incorrect-iss-field" arguments="value">
<p>
The <info:var>value</info:var> of the iss field is incorrect.
</p>
</info:deftp>
<info:deftp type="exception type" name="&incorrect-aud-field" arguments="value">
<p>
The <info:var>value</info:var> of the aud field is incorrect.
</p>
</info:deftp>
<info:deftp type="exception type" name="&incorrect-iat-field" arguments="value">
<p>
The <info:var>value</info:var> of the iat field is incorrect.
</p>
</info:deftp>
<info:deftp type="exception type" name="&incorrect-exp-field" arguments="value">
<p>
The <info:var>value</info:var> of the exp field is incorrect.
</p>
</info:deftp>
<info:deftp type="exception type" name="&incorrect-cnf/jkt-field" arguments="value">
<p>
The <info:var>value</info:var> of the cnf/jkt field is incorrect.
</p>
</info:deftp>
<info:deftp type="exception type" name="&incorrect-client-id-field" arguments="value">
<p>
The <info:var>value</info:var> of the client-id field is incorrect.
</p>
</info:deftp>
<info:deftp type="exception type" name="&incorrect-redirect-uris-field" arguments="value">
<p>
The <info:var>value</info:var> of the redirect-uris field of a
client manifest is incorrect.
</p>
</info:deftp>
<info:deftp type="exception type" name="&incorrect-typ-field" arguments="value">
<p>
The <info:var>value</info:var> of the typ field in the DPoP proof
header is incorrect.
</p>
</info:deftp>
<info:deftp type="exception type" name="&incorrect-jwk-field" arguments="value cause">
<p>
The <info:var>value</info:var> of the jwk field in the DPoP
proof header is incorrect.
</p>
</info:deftp>
<info:deftp type="exception type" name="&incorrect-jti-field" arguments="value">
<p>
The <info:var>value</info:var> of the jti field in the DPoP
proof is incorrect.
</p>
</info:deftp>
<info:deftp type="exception type" name="&incorrect-nonce-field" arguments="value">
<p>
The <info:var>value</info:var> of the nonce field in the DPoP
proof is incorrect.
</p>
</info:deftp>
<info:deftp type="exception type" name="&incorrect-htm-field" arguments="value">
<p>
The <info:var>value</info:var> of the htm field in the DPoP
proof is incorrect.
</p>
</info:deftp>
<info:deftp type="exception type" name="&incorrect-htu-field" arguments="value">
<p>
The <info:var>value</info:var> of the htu field in the DPoP
proof is incorrect.
</p>
</info:deftp>
<info:deftp type="exception type" name="&not-an-access-token" arguments="value cause">
<p>
The <info:var>value</info:var> is not an access token.
</p>
</info:deftp>
<info:deftp type="exception type" name="&not-an-access-token-header" arguments="value cause">
<p>
The <info:var>value</info:var> is not an access token header.
</p>
</info:deftp>
<info:deftp type="exception type" name="&not-an-access-token-payload" arguments="value cause">
<p>
The <info:var>value</info:var> is not an access token payload.
</p>
</info:deftp>
<info:deftp type="exception type" name="&cannot-fetch-issuer-configuration" arguments="issuer cause">
<p>
It is impossible to fetch the configuration of
<info:var>issuer</info:var>.
</p>
</info:deftp>
<info:deftp type="exception type" name="&cannot-fetch-jwks" arguments="issuer uri cause">
<p>
It is impossible to fetch the keys of
<info:var>issuer</info:var> at <info:var>uri</info:var>.
</p>
</info:deftp>
<info:deftp type="exception type" name="&cannot-decode-access-token" arguments="value cause">
<p>
The <info:var>value</info:var> string is not an encoding of a
valid access token.
</p>
</info:deftp>
<info:deftp type="exception type" name="&cannot-encode-access-token" arguments="access-token key cause">
<p>
The <info:var>access-token</info:var> cannot be signed.
</p>
</info:deftp>
<info:deftp type="exception type" name="&not-a-dpop-proof" arguments="value cause">
<p>
The <info:var>value</info:var> is not a DPoP proof.
</p>
</info:deftp>
<info:deftp type="exception type" name="&not-a-dpop-proof-header" arguments="value cause">
<p>
The <info:var>value</info:var> is not a DPoP proof header.
</p>
</info:deftp>
<info:deftp type="exception type" name="&not-a-dpop-proof-payload" arguments="value cause">
<p>
The <info:var>value</info:var> is not a DPoP proof payload.
</p>
</info:deftp>
<info:deftp type="exception type" name="&dpop-method-mismatch" arguments="signed requested">
<p>
The method value <info:var>signed</info:var> in the DPoP proof
does not match the method that is
<info:var>requested</info:var> on the server.
</p>
</info:deftp>
<info:deftp type="exception type" name="&dpop-uri-mismatch" arguments="signed requested">
<p>
The URI value <info:var>signed</info:var> in the DPoP proof
does not match the URI that is <info:var>requested</info:var>
on the server.
</p>
</info:deftp>
<info:deftp type="exception type" name="&dpop-signed-in-future" arguments="signed current">
<p>
The proof is <info:var>signed</info:var> for a date which is
too much ahead of the <info:var>current</info:var> time.
</p>
</info:deftp>
<info:deftp type="exception type" name="&dpop-too-old" arguments="signed current">
<p>
The proof was <info:var>signed</info:var> at a past date of
<info:var>current</info:var>.
</p>
</info:deftp>
<info:deftp type="exception type" name="&dpop-unconfirmed-key" arguments="key expected cause">
<p>
The confirmation of <info:var>key</info:var> is not what is
<info:var>expected</info:var>, or (if a function was passed as
<info:var>cnf/check</info:var>) the <info:var>cause</info:var>
exception occurred while confirming.
</p>
</info:deftp>
<info:deftp type="exception type" name="&jti-found" arguments="jti cause">
<p>
The <info:var>jti</info:var> of the proof has already been
issued in a recent past.
</p>
</info:deftp>
<info:deftp type="exception type" name="&cannot-decode-dpop-proof" arguments="value cause">
<p>
The <info:var>value</info:var> string is not an encoding of a
valid DPoP proof.
</p>
</info:deftp>
<info:deftp type="exception type" name="&cannot-encode-dpop-proof" arguments="dpop-proof key cause">
<p>
The <info:var>dpop-proof</info:var> cannot be signed.
</p>
</info:deftp>
<info:deftp type="exception type" name="&cannot-fetch-linked-data" arguments="uri cause">
<p>
Could not fetch the graph referenced by
<info:var>uri</info:var>.
</p>
</info:deftp>
<info:deftp type="exception type" name="&not-a-client-manifest" arguments="value cause">
<p>
The <info:var>client-manifest</info:var> is incorrect.
</p>
</info:deftp>
<info:deftp type="exception type" name="&unauthorized-redirection-uri" arguments="manifest uri">
<p>
The authorization <info:var>uri</info:var> is not advertised
in <info:var>manifest</info:var>.
</p>
</info:deftp>
<info:deftp type="exception type" name="&cannot-serve-public-manifest" arguments="">
<p>
You cannot serve the public client manifest.
</p>
</info:deftp>
<info:deftp type="exception type" name="&no-client-manifest-registration" arguments="id">
<p>
The <info:var>id</info:var> client manifest does not have a
registration triple in its document.
</p>
</info:deftp>
<info:deftp type="exception type" name="&inconsistent-client-manifest-id" arguments="id advertised-id">
<p>
The client <info:var>manifest</info:var> is being fetched at
<info:var>id</info:var>, but it is valid for another client
<info:var>advertised-id</info:var>.
</p>
</info:deftp>
<info:deftp type="exception type" name="&cannot-fetch-client-manifest" arguments="id cause">
<p>
Could not fetch a client manifest at <info:var>id</info:var>.
</p>
</info:deftp>
<info:deftp type="exception type" name="&not-an-authorization-code" arguments="value cause">
<p>
The <info:var>value</info:var> is not an authorization code.
</p>
</info:deftp>
<info:deftp type="exception type" name="&not-an-authorization-code-header" arguments="value cause">
<p>
The <info:var>value</info:var> is not an authorization code header.
</p>
</info:deftp>
<info:deftp type="exception type" name="&not-an-authorization-code-payload" arguments="value cause">
<p>
The <info:var>value</info:var> is not an authorization code payload.
</p>
</info:deftp>
<info:deftp type="exception type" name="&authorization-code-expired" arguments="exp current-time">
<p>
The authorization code has expired at
<info:var>exp</info:var>, it is now
<info:var>current-time</info:var>.
</p>
</info:deftp>
<info:deftp type="exception type" name="&cannot-decode-authorization-code" arguments="value cause">
<p>
The <info:var>value</info:var> string is not an encoding of a
valid authorization code.
</p>
</info:deftp>
<info:deftp type="exception type" name="&cannot-encode-authorization-code" arguments="authorization-code key cause">
<p>
The <info:var>authorization-code</info:var> cannot be signed.
</p>
</info:deftp>
<info:deftp type="exception type" name="&invalid-refresh-token" arguments="refresh-token">
<p>
The <info:var>refresh-token</info:var> is unknown to the
identity provider.
</p>
</info:deftp>
<info:deftp type="exception type" name="&invalid-key-for-refresh-token" arguments="key jkt">
<p>
The refresh token was issued for <info:var>jkt</info:var>, but
it is used with <info:var>key</info:var>.
</p>
</info:deftp>
<info:deftp type="exception type" name="&not-an-id-token" arguments="value cause">
<p>
The <info:var>value</info:var> is not an ID token.
</p>
</info:deftp>
<info:deftp type="exception type" name="&not-an-id-token-header" arguments="value cause">
<p>
The <info:var>value</info:var> is not an ID token header.
</p>
</info:deftp>
<info:deftp type="exception type" name="&not-an-id-token-payload" arguments="value cause">
<p>
The <info:var>value</info:var> is not an ID token payload.
</p>
</info:deftp>
<info:deftp type="exception type" name="&cannot-decode-id-token" arguments="value cause">
<p>
The <info:var>value</info:var> string is not an encoding of a
valid ID token.
</p>
</info:deftp>
<info:deftp type="exception type" name="&cannot-encode-id-token" arguments="id-token key cause">
<p>
The <info:var>id-token</info:var> cannot be signed.
</p>
</info:deftp>
<info:deftp type="exception type" name="&unknown-client-locale" arguments="web-locale c-locale">
<p>
The <info:var>web-locale</info:var> of the client, translated
to C as <info:var>c-locale</info:var>, cannot be set. This
exception is always continuable; if the handler returns, then
the page will be served in the english locale.
</p>
</info:deftp>
<info:deftp type="exception type" name="&unsupported-grant-type" arguments="value">
<p>
The token request failed to indicate a
<info:var>value</info:var> for the grant type, or indicated an
unsupported grant type.
</p>
</info:deftp>
<info:deftp type="exception type" name="&no-authorization-code" arguments="">
<p>
The token request forgot to put an authorization code.
</p>
</info:deftp>
<info:deftp type="exception type" name="&no-refresh-token" arguments="">
<p>
The token request forgot to put a refresh token with the
request.
</p>
</info:deftp>
<info:deftp type="exception type" name="&unconfirmed-provider" arguments="subject provider">
<p>
<info:var>provider</info:var> is not confirmed by
<info:var>subject</info:var> as an identity provider.
</p>
</info:deftp>
<info:deftp type="exception type" name="&no-provider-candidates" arguments="webid causes">
<p>
The <info:var>webid</info:var> cannot be certified by any
identity providers. The <info:var>causes</info:var> alist
indicates an error for each candidates.
</p>
</info:deftp>
<info:deftp type="exception type" name="&neither-identity-provider-nor-webid" arguments="uri why-not-identity-provider why-not-webid">
<p>
The <info:var>uri</info:var> you passed to get an
authorization code is neither an identity provider (because
<info:var>why-not-identity-provider</info:var>) nor a webid
(because <info:var>why-not-webid</info:var>).
</p>
</info:deftp>
<info:deftp type="exception type" name="&token-request-failed" arguments="cause">
<p>
The token request failed on the server.
</p>
</info:deftp>
<info:deftp type="exception type" name="&profile-not-found" arguments="webid iss dir">
<p>
The <info:var>webid</info:var>, as certified by
<info:var>iss</info:var>, cannot be refreshed because we don’t
have a refresh token stored in <info:var>dir</info:var>.
</p>
</info:deftp>
<h1>Running an Identity Provider</h1>
<p>
This project is packaged with a barebones identity provider. It
has an authorization endpoint and a token endpoint (and it
serves its public keys), but it is only intended for one
specific person.
</p>
<p>
You can start it by invoking the <pre>webid-oidc-issuer</pre>
program, with the following options:
</p>
<ul>
<li>
<pre>-h</pre>, or <pre>--help</pre> prints a summary of
options and exit.
</li>
<li>
<pre>-v</pre>, or <pre>--version</pre> prints the version of
the program and exits.
</li>
<li>
<pre>-i <info:var>URI</info:var></pre>, or
<pre>--issuer=<info:var>URI</info:var></pre> sets the global
server name of the identity provider. It should have an empty
path.
</li>
<li>
<pre>-k <info:var>FILE.jwk</info:var></pre>, or
<pre>--key-file=<info:var>FILE.jwk</info:var></pre> sets the
file name where to read or generate a key for the identity
provider. This file should be JSON, containing the
representation of a JWK key pair.
</li>
<li>
<pre>-s <info:var>WEBID</info:var></pre>, or
<pre>--subject=<info:var>WEBID</info:var></pre> sets the webid
of the only user of the identity provider. This is an URI,
pointing to a RDF node corresponding to the user’s profile.
</li>
<li>
<pre>-w <info:var>PASSWORD</info:var></pre>, or
<pre>--password=<info:var>PASSWORD</info:var></pre>, sets the
password that the user must enter to authorize an
application.
</li>
<li>
<pre>-j <info:var>URI</info:var></pre>, or
<pre>--jwks-uri=<info:var>URI</info:var></pre> tells the
server that requests to <info:var>URI</info:var> should be
responded with the public key used to sign the tokens.
</li>
<li>
<pre>-a <info:var>URI</info:var></pre>, or
<pre>--authorization-endpoint-uri=<info:var>URI</info:var></pre>
tells the server that requests to <info:var>URI</info:var>
should be treated as authorization requests.
</li>
<li>
<pre>-t <info:var>URI</info:var></pre>, or
<pre>--token-endpoint-uri=<info:var>URI</info:var></pre> tells
the server that requests to <info:var>URI</info:var> should be
treated as token negociation requests.
</li>
<li>
<pre>-p <info:var>PORT</info:var></pre>, or
<pre>--port=<info:var>PORT</info:var></pre>, change the port
number used by the server. By default, it is set to 8080.
</li>
<li>
<pre>-l <info:var>FILE.log</info:var></pre>, or
<pre>--log-file=<info:var>FILE.log</info:var></pre> let the
server dump all its output to
<info:var>FILE.log</info:var>. Since I don’t know how to deal
with syslog, this is the only way to keep logs with a shepherd
service.
</li>
<li>
<pre>-e <info:var>FILE.err</info:var></pre>, or
<pre>--error-file=<info:var>FILE.err</info:var></pre> let the
server dump all its errors to <info:var>FILE.err</info:var>.
</li>
</ul>
<p>
The program is sensitive to the environment variables. The most
important one is <emph>LANG</emph>, which influences how the
program is internationalized to the server administrator (the
pages served to the user use the user agent’s locale). This
changes the long form of the options, and the language in the
log files.
</p>
<p>
The <emph>XDG_DATA_HOME</emph> should point to some place where
the program will store refresh tokens, under the
<pre>webid-oidc</pre> directory. For a system service, you might
want to define that environment to <pre>/var/lib</pre>, for
instance.
</p>
<p>
The <emph>XDG_CACHE_HOME</emph> should point to a directory
where to store the seed of the random number generator (under a
<pre>webid-oidc</pre> directory, again). Changing the seed only
happens when a program starts to require the random number
generator. You can safely delete this directory, but you need to
restart the program to actually change the seed.
</p>
<h1>Running a Resource Server</h1>
<p>
A Solid server is the server that manages your data. It needs to
check that the proofs of possession are correct, and the
possessed key is signed by the identity provider.
</p>
<h2>Running webid-oidc-reverse-proxy</h2>
<p>
The distribution comes with a reverse proxy, aptly named
<pre>webid-oidc-reverse-proxy</pre>, to listen to an interface,
take requests, authenticate them, and pass them to a backend
with an additional header containing the webid of the agent, if
authenticated.
</p>
<p>The reverse proxy is invoked with the following arguments:</p>
<ul>
<li>
<pre>-p</pre> <info:var>PORT</info:var>,
<pre>--port=</pre><info:var>PORT</info:var>: the port on which
the reverse proxy listens;
</li>
<li>
<pre>-i</pre> <info:var>INBOUND</info:var>,
<pre>--inbound-uri=</pre><info:var>INBOUND</info:var>: the
public name of the server;
</li>
<li>
<pre>-o</pre> <info:var>OUTBOUND</info:var>,
<pre>--outbound-uri=</pre><info:var>OUTBOUND</info:var>: the
address of the backend;
</li>
<li>
<pre>-H</pre> <info:var>HEADER</info:var>,
<pre>--header=</pre><info:var>HEADER</info:var>: replace the
name of the header that will contain the webid of the
user. Defaults to <pre>XXX-Agent</pre>. Please note that this
value should be ASCII, otherwise it’s not guaranteed that the
reverse proxy will drop other capitalizations of the header in
malicious requests.
</li>
<li>
<pre>-l <info:var>FILE.log</info:var></pre>, or
<pre>--log-file=<info:var>FILE.log</info:var></pre> let the
server dump all its output to
<info:var>FILE.log</info:var>. See the identity provider
comment.
</li>
<li>
<pre>-e <info:var>FILE.err</info:var></pre>, or
<pre>--error-file=<info:var>FILE.err</info:var></pre> let the
server dump all its errors to <info:var>FILE.err</info:var>.
</li>
</ul>
<p>
You can localize the interface by setting the
<info:var>LANG</info:var> environment variable.
</p>
<h2>The authenticator</h2>
<p>
In <emph>(webid-oidc jws)</emph>, the following function
gives a simple API for a web server:
</p>
<info:deffn type="function"
name="make-authenticator"
arguments="jti-list [#server-uri] [#current-time] [#http-get]">
<p>
Create an authenticator, i.e. a function that takes a request
and request body and returns the webid of the authenticated
user, or <pre>#f</pre> if it is not authenticated.
</p>
<p>
To prevent replay attacks, each request is signed by the
client with a different unique padding value. If such a value
has already been seen, then the request must fail.
</p>
<p>
The authenticator expects the client to demonstrate the
possession of a key that the identity provider knows. So the
client creates a DPoP proof, targetted to a specific URI. In
order to check that the URI is correct, the authenticator
needs the public URI of the service.
</p>
<p>
The JTIs are checked within a small time frame. By default,
the system time will be used. Otherwise, you can customize the
<pre>current-time</pre> optional keyword argument, to pass a
thunk returning a time from <emph>(srfi srfi-19)</emph>.
</p>
<p>
You may want to customize the <info:var>http-get</info:var>
optional keyword argument to pass a function to replace
<pre>http-get</pre> from <emph>(http client)</emph>. This
function takes an URI and optional <pre>#:headers</pre>
arguments, makes the request, and return two values: the
response, and the response body.
</p>
<p>
This function, in
<emph>(webid-oidc resource-server)</emph>, returns a web
request handler, taking the request and request body, and
returning the subject of the access token. If an error
happens, it is thrown; the function always returns a valid
URI.
</p>
</info:deffn>
<h1>Running a client</h1>
<p>
To run a client, you need to proceed in two steps. First,
acquire an OIDC ID token and an access token from the identity
provider, and then present the access token and a proof of
possession of the linked key in each request, in a DPoP HTTP
header.
</p>
<p>
The first operation is performed by the
<emph>(webid-oidc client)</emph> module.
</p>
<info:deffn type="function" name="authorize" arguments="host/webid #client-id #redirect-uri [#state] [#http-get]">
<p>
The user enters a valid webid or a host name, and then this
function will query it (with the <info:var>http-get</info:var>
parameter, by default the web client from
<emph>(web client)</emph>) to determine the authorization
endpoint. The function will return an alist of authorization
URIs, indexed by approved identity provider URIs, that the
user should browse with a traditional web browser.
</p>
<p>
Each application should have its own webid, or in that case
<info:var>client-id</info:var>, that can be dereferenced by
the identity provider.
</p>
<p>
Once the user has given authorization, the user’s agent will
be redirected to <info:var>redirect-uri</info:var>, with the
authorization code as a GET parameter. It is possible to pass
a <info:var>state</info:var>, but this is optional.
</p>
</info:deffn>
<p>
Once the client gets the authorization code, it is necessary to
create an access token and ID token.
</p>
<info:deffn type="function" name="token" arguments="host client-key [#authorization-code] [#refresh-token] [#http-get] [#http-post] [#current-time]">
<p>
Trade an <info:var>authorization-code</info:var>, or a
<info:var>refresh-token</info:var>, for an ID token and an
access token bound to the <info:var>client-key</info:var>
issued by <info:var>host</info:var>, the identity provider.
</p>
<p>
You can override the HTTP client used
(<info:var>http-get</info:var> and
<info:var>http-post</info:var>), and how to compute the time
(<info:var>current-time</info:var>).
</p>
</info:deffn>
<p>
In an application, you would have a list of profiles in
XDG_DATA_HOME, consisting of triples (webid, issuer, refresh
token).
</p>
<info:deffn type="function" name="list-profiles" arguments="[#dir]">
<p>
Read the list of available profiles. Returns a list of
triples, webid, issuer, reresh token.
</p>
<p>
By default, this function will look for the profiles file in
XDG_DATA_HOME. You can bypass it by providing the
<info:var>#dir</info:var> optional keyword argument.
</p>
</info:deffn>
<info:deffn type="function" name="setup" arguments="get-host/webid choose-provider browse-authorization-uri #client-id #redirect-uri [#dir] [#http-get] [#http-post] [#current-time]">
<p>
Negociate a refresh token, and save it. The function returns 3
values: the decoded ID token pyload, the encoded access token
and the key pair.
</p>
<p>
The <info:var>get-host/webid</info:var> thunk should ask the
user’s webid or identity provider, and return
it. <info:var>choose-provider</info:var> is called with a list
of possible identity providers as host names (strings), and
the user should choose one. The chosen one is
returned. Finally,
<info:var>browse-authorization-uri</info:var> should ask or
let the user browse an URI as its argument, and return the
authorization code taken from the redirect URI.
</p>
<p>
The refresh token is saved to disk, as a profile, in
XDG_DATA_HOME. Pass the optional <info:var>#dir</info:var>
keyword argument to override the location.
</p>
<p>
You need to set <info:var>client-id</info:var> to the public
webid of the app, and <info:var>redirect-uri</info:var> to one
of the approved redirection URIs for the application ID.
</p>
</info:deffn>
<info:deffn type="function" name="login" arguments="webid issuer refresh-token key [#dir] [#http-get] [#http-post] [#current-time]">
<p>
If you have already a known profile, you can use it to
automatically log in. This function might update the refresh
token if it changed, so you can again set
<info:var>#dir</info:var>. Please note that the
<info:var>refresh-token</info:var> is bound to the client
<info:var>key</info:var> on server side, so you must always
use the same <info:var>key</info:var>.
</p>
</info:deffn>
<info:deffn type="function" name="refresh" arguments="id-token key [#dir] [#http-get] [#http-post] [#current-time]">
<p>
If you have an ID token bound to a known profile, this helper
function will look up the associated refresh token and log in.
</p>
</info:deffn>
<info:deffn type="function" name="make-client" arguments="id-token access-token key [#dir] [#http-get] [#http-post] [#http-request] [#current-time]">
<p>
Return a replacement of <pre>http-request</pre> from
<emph>(web client)</emph>, that automatically signs
requests and refresh the tokens when needed.
</p>
<p>
<info:var>#http-get</info:var> and
<info:var>#http-post</info:var> are only used to refresh the
tokens, while <info:var>#http-request</info:var> is used as a
back-end for the requests.
</p>
<p>
<info:var>#current-time</info:var> is set to a thunk that
returns the time. It is used to issue DPoP proofs.
</p>
</info:deffn>
<p>
The identity provider needs to call the application on the
web. So, your client should have a public endpoint on the web.
</p>
<info:deffn type="function" name="serve-application" arguments="id redirect-uri [#client-name] [#client-uri]">
<p>
Return a handler for web requests to serve the application
manifest and the redirection to transmit the authorization
code. You should set the <info:var>client-name</info:var> to
your application name and <info:var>client-uri</info:var> to
point to where to a presentation of your application.
</p>
</info:deffn>
<p>
The <pre>webid-oidc-client-service</pre> program can run a
server to serve these resources. It is invoked with the
following options:
</p>
<ul>
<li>
<pre>-h</pre>, or <pre>--help</pre> prints a summary of the
options and exit.
</li>
<li>
<pre>-v</pre>, or <pre>--version</pre> prints the version of
the program and exits.
</li>
<li>
<pre>-i <info:var>URI</info:var></pre>, or
<pre>--client-id=<info:var>URI</info:var></pre> sets the
global identitifier of the application, which is dereferenced
to a semantic resource.
</li>
<li>
<pre>-r <info:var>URI</info:var></pre>, or
<pre>--redirect-uri=<info:var>URI</info:var></pre> sets the
redirection URI.
</li>
<li>
<pre>-n <info:var>NAME</info:var></pre>, or
<pre>--client-name=<info:var>NAME</info:var></pre> sets the
name of your application, so that it is shown when the user
gets an authorization. The webid-oidc issuer program that
comes with this package does not display it, because it could
be dishonest, but other implementations might.
</li>
<li>
<pre>-u <info:var>URI</info:var></pre>, or
<pre>--client-uri=<info:var>URI</info:var></pre>, sets an URI
for the identity provider to learn more about your app.
</li>
<li>
<pre>-p <info:var>PORT</info:var></pre>, or
<pre>--port=<info:var>PORT</info:var></pre>, change the port
number used by the server. By default, it is set to 8080.
</li>
<li>
<pre>-l <info:var>FILE.log</info:var></pre>, or
<pre>--log-file=<info:var>FILE.log</info:var></pre> let the
server dump all its output to <info:var>FILE.log</info:var>.
</li>
<li>
<pre>-e <info:var>FILE.err</info:var></pre>, or
<pre>--error-file=<info:var>FILE.err</info:var></pre> let the
server dump all its errors to <info:var>FILE.err</info:var>.
</li>
</ul>
<p>
The program is sensitive to the environment variable
<emph>LANG</emph>, which influences how the program is
internationalized to the server administrator. This changes the
long form of the options, and the language in the log files.
</p>
<h1 type="appendix">GNU Free Documentation License</h1>
<info:gfdl />
<h1 type="unnumbered">Index</h1>
<info:printindex />
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