     [file version.texi not included]

This is the manual of disfluid (version VERSION, UPDATED), an implementation of the Solid authentication protocol for guile, client and server.

Copyright © 2020, 2021 Vivien Kraus

     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''

Disfluid
********

Decentralized Authentication on the Web
***************************************

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 USEFUL-PROGRAM wants to authenticate MEGACORP users, then USEFUL-PROGRAM has to register to MEGACORP first, and get approved. This goes against the principle of permission-less innovation, which is at the heart of the web.

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.

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.

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.

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.

Invoking disfluid
*****************

The disfluid program provides different modes of operations:

reverse-proxy
     Run an authenticating reverse proxy. With this command, you specify a backend server. When an authenticated user makes a request, you receive an additional header containing the user’s identity.

identity-provider
     Run the identity provider only.

client-service
     The client applications must serve some resources: namely, the client manifest and the redirect URI.

server
     Run both an identity provider and a resource server.

The server is configured with command-line arguments, and environment variables.

General options
===============

The server will respond to -h and -v commands, to get the help output and the version information.

The server output (command-line, logs) are localized for the system administrator. You can control it with the LANG environment variable. So if your locale is not English, you can have the same commands as in this manual by running with LANG=C.

The programs respect the XDG_DATA_HOME and XDG_CACHE_HOME to store persistent data and disposable data. The cache directory can be deleted at any time. If one of these variables is not set, its value is computed from the HOME environment variable.

General server configuration
============================

All servers are published under the Affero GPL, which means that the service provider needs to publish all changes made to the program to users over the network. The disfluid command provides a --complete-corresponding-source option so that the system administrator can specify a means to download the source.

The servers will add a Source: header in each response, containing the value of this configuration option.

The servers can be configured to redirect output and errors to a log file and an error file, with the --log-file and --error-file options.

The server will listen to port 8080 by default, but this may be configured with --port. Since the servers do not support TLS, and they only support HTTP/1.1, they are intended to run behind a reverse proxy (even for the authenticating reverse proxy).

Finally, the servers are required to know their public name. This is configured with the --server-name option.

The server will make requests on the world-wide web, for instance to download client manifests. The requests can be redirected with XML Catalog, by setting the XML_CATALOG_FILES to a space-separated list of URIs (can be file: URIs). The requests cannot be directed to the file system.

Configuration for the resource server
=====================================

The reverse proxy sets an identity header to authenticated requests. By default, it is XXX-Agent, but it can be configured with --header.

The reverse proxy is configured to contact a backend URI with --backend-uri. This backend URI should not be directly exposed, because a malicious user could set the identity header.

Configuration for the identity provider
=======================================

The identity provider can only handle one user. If you want to handle multiple users, it is highly advised to use a different host name for each user, in case the server is accessed from a web browser. You can set the identity of the user with --subject, and write the user’s password in a file. Pass the file name with --encrypted-password-file. You can pass the encrypted password directly with --encrypted-password, but the encrypted password will be public.

The encrypted password format is defined by the crypt function in the C library. For glibc, it looks like this: $N$SALT$HASH, where N is the algorithm identifier, SALT is the password salt annd HASH is its hash.

The server uses a key, which is not the same thing as the TLS certificate of the server (remember, the servers don’t support TLS). It is in the JWK format. You set its file name with --key-file. If the key file does not exist, it will be generated.

Finally, the public openid configuration requires you to set the JWKS URI (--jwks-uri), authorization endpoint URI (--authorization-endpoint-uri) and token endpoint URI (--token-endpoint-uri). The identity provider will publish the full URIs, but will respond to their path, regardless of the host.

Configuration for the client service
====================================

The client will serve a stupid page for the redirect URI that will only display the authorization code. The redirect URI is set with --redirect-uri.

The client ID is set with --client-id. This is the URI under which the client registrationn is served.

Finally, you can set some cosmetic options, but since it can confuse the user, they are hidden by default by the identity provider.

--client-name
     set the name of the application.

--client-uri
     set an URI where to find more information about the client.

Running disfluid with GNU Guix
******************************

The channel at https://labo.planete-kraus.eu/webid-oidc-channel.git can be used with guix. It defines the package at the latest commit, and a service definition in (vkraus services disfluid).

 -- service type: disfluid-service-type
     This service runs a bunch of disfluid servers with the disfluid system user, each with a unique name. The value it takes is an alist of service configurations: the keys are unique names (to differenciate the generated shepherd services), and the values are configuration records for an issuer, reverse proxy, server, or client service.

 -- configuration record: <disfluid-issuer-configuration> [DISFLUID] COMPLETE-CORRESPONDING-SOURCE ISSUER KEY-FILE SUBJECT ENCRYPTED-PASSWORD-FILE JWKS-URI AUTHORIZATION-ENDPOINT-URI TOKEN-ENDPOINT-URI PORT [EXTRA-OPTIONS]
     The configuration for the identity provider. The optional DISFLUID argument is the package containing the binary to run, if you want to apply some patches, and EXTRA-OPTIONS is an empty list by default.

 -- configuration record: <disfluid-reverse-proxy-configuration> [DISFLUID] COMPLETE-CORRESPONDING-SOURCE PORT INBOUND-URI OUTBOUND-URI HEADER [EXTRA-OPTIONS]
     This record configures an authenticating reverse proxy.

 -- configuration record: <disfluid-client-service-configuration> [DISFLUID] COMPLETE-CORRESPONDING-SOURCE CLIENT-ID REDIRECT-URI [CLIENT-NAME] [CLIENT-URI] PORT [EXTRA-OPTIONS]
     This record configures a server to serve public application pages.

 -- configuration record: <disfluid-server-configuration> [DISFLUID] COMPLETE-CORRESPONDING-SOURCE SERVER-NAME KEY-FILE SUBJECT ENCRYPTED-PASSWORD-FILE JWKS-URI AUTHORIZATION-ENDPOINT-URI TOKEN-ENDPOINT-URI PORT [EXTRA-OPTIONS]
     The configuration for the full server.

The Json Web Token
******************

The Json Web Token, or JWT, is a terse representation of a pair of JSON objects: the header, and the payload. The JWT can be encoded as a Json Web Signature (JWS), 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.

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 symbols to values, arrays are vectors. It is unfortunate that guile-json has a slightly different representation, where alist keys are strings, but we hope that in the future SRFI-180 will be more closely respected.

The ID token
============

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:

webid
     the URI of the user’s webid;

iss
     the URI of the identity provider (issuer);

sub
     the username (the webid-oidc issuer puts the webid again here, but it could be any string);

aud
     the ID of the client application that is intended to receive the ID token;

nonce
     some random data to change the signature;

exp
     an UTC time (in seconds) for when the token expires;

iat
     the time when it was issued.

There are functions to work with ID tokens in (webid-oidc oidc-id-token).

 -- function: id-token? OBJECT
     Check that OBJECT is a decoded ID token.

The following helper functions convert URIs to the URIs from (web uri) and times to (srfi srfi-19) dates.

 -- function: id-token-webid TOKEN
 -- function: id-token-iss TOKEN
 -- function: id-token-sub TOKEN
 -- function: id-token-aud TOKEN
 -- function: id-token-nonce TOKEN
 -- function: id-token-exp TOKEN
 -- function: id-token-iat TOKEN
     Get the suitable field from the payload of TOKEN.

ID tokens can be signed and encoded as a string, or decoded.

 -- function: id-token-decode TOKEN [#HTTP-GET]
     Decode TOKEN, 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 http-get optional keyword argument can set a different implementation of http-get from (web client). Return #f if it failed, or the decoded token otherwise.

 -- function: id-token-encode TOKEN KEY
     Encode TOKEN and sign it with the issuer’s KEY.

 -- function: issue-id-token ISSUER-KEY #:ALG #:WEBID #:ISS #:SUB #:AUD #:VALIDITY
     Create an ID token that is valid for #:VALIDITY seconds, and encode it with ISSUER-KEY.

The access token
================

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.

The API is defined in (webid-oidc access-token).

 -- function: access-token? OBJECT
     Check that OBJECT is a decoded access token.

There are field getters for the access token:

 -- function: access-token-webid TOKEN
 -- function: access-token-iss TOKEN
 -- function: access-token-aud TOKEN
 -- function: access-token-exp TOKEN
 -- function: access-token-iat TOKEN
 -- function: access-token-cnf/jkt TOKEN
 -- function: access-token-client-id TOKEN
     Get the suitable field from the payload of TOKEN.

Access tokens can be signed and encoded as a string, or decoded.

 -- function: access-token-decode TOKEN [#HTTP-GET]
     Decode TOKEN, 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 http-get optional keyword argument can set a different implementation of http-get from (web client), for instance to re-use the what has been obtained by the ID token validation. Return the decoded access token, or raise an exception.

 -- function: issue-access-token ISSUER-KEY #ALG #WEBID #ISS #:VALIDITY [#CLIENT-KEY | #CNF/JKT] #CLIENT-ID
     Create an access token for #:VALIDITY seconds, and encode it with ISSUER-KEY. You can either set the #:cnf/jkt keyword argument with the fingerprint of the client key, or set #:client-key directly, in which case the fingerprint will be computed for you.

The DPoP proof
==============

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.

 -- function: dpop-proof? PROOF
     Check that the PROOF is a decoded DPoP proof. The validity of the proof is not checked by this function.

 -- function: dpop-proof-alg PROOF
 -- function: dpop-proof-jwk PROOF
 -- function: dpop-proof-jti PROOF
 -- function: dpop-proof-htm PROOF
 -- function: dpop-proof-htu PROOF
 -- function: dpop-proof-iat PROOF
 -- function: dpop-proof-ath PROOF
     Get the corresponding field of the proof.

 -- function: dpop-proof-decode METHOD URI STR CNF/CHECK [#:ACCESS-TOKEN]
     Check and decode a DPoP proof encoded as STR.

     In order to prevent replay attacks, each proof has a unique random string that is remembered globally until its expiration date is reached.

     The proof is limited to the scope of one URI and one METHOD ('GET, 'POST and so on).

     The key that is used to sign the proof should be confirmed by the identity provider. To this end, the CNF/CHECK function is called with the fingerprint of the key. The function should check that the fingerprint is OK (return a boolean).

     Finally, when the DPoP proof is tied to an access token (so, for all uses except requesting an access token or a refresh token), it must be bound to an ACCESS-TOKEN.

The DPoP proof algorithm is sensitive to the current time, because the proofs have a limited time validity. By default, the time is the system time when the proof is decoded.

 -- parameter: current-date
     This parameter overrides the current time.

     It is a thunk returning a date, so you need to put two parenthesis to get the time. However, you can set it to a date, a time, a number of seconds, or a thunk returning any of these.

              (use-module ((webid-oidc parameters) #:prefix p:))
              ;; This is the current date:
              ((p:current-date))
              ;; You can override it with a thunk, or a fixed date:
              (parameterize ((p:current-date 0))
                ;; Jan 1st 1970
                ((p:current-date)))

 -- function: dpop-proof-encode PROOF KEY
     Encode the proof and sign it with KEY. To generate valid proofs, KEY should be the private key corresponding to the jwk field of the proof.

 -- function: issue-dpop-proof CLIENT-KEY #ALG #HTM #HTU [#:ACCESS-TOKEN=#f]
     Create a proof, sign it and encode it with CLIENT-KEY. CLIENT-KEY 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. For most uses, the DPoP proof should be encoded for a specific access token. Only token requests should omit the access-token field.

     The iat field of the DPoP proof is read from the CURRENT-DATE parameter.

Generic JWTs
============

You can parse generic JWTs signed with JWS with the following functions from (webid-oidc jws).

 -- function: jws? JWT
     Check that JWT is a decoded JWT signed with JWS.

 -- function: jws-alg JWT
     Get the algorithm used to sign JWT.

 -- function: jws-decode STR LOOKUP-KEYS
     Check and decode a JWT signed with JWS and encoded as STR.

     Since the decoding and signature verification happen at the same time (for user friendliness), the LOOKUP-KEYS 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.

 -- function: jws-encode JWT KEY
     Encode the JWT and sign it with KEY.

Public-key cryptography
=======================

Some functions require a key, or a key pair, to operate. The (webid-oidc jwk) module provides you with everything required to manage keys.

 -- Class: <private-key> ()
     This is the base class for a private key. You need it to issue signatures.

 -- Class: <public-key> ()
     This is the base class for a public key. You need it to check signatures.

 -- Class: <key-pair> () PUBLIC-KEY PRIVATE-KEY
     A key pair contains a PUBLIC-KEY and a matching PRIVATE-KEY. You use this form for keys you own.

 -- Class: <rsa-key-pair> () (<key-pair>)
     This key pair contains matching RSA keys.

 -- Class: <ec-key-pair> () (<key-pair>) CRV
     This key pair contains matching elliptic curve keys. CRV is a symbol identifiying the curve.

 -- Class: <rsa-private-key> (<private-key>) D P Q DP DQ QI
 -- Class: <rsa-public-key> (<public-key>) N E
 -- Class: <ec-scalar> (<private-key>) CRV Z
 -- Class: <ec-point> (<public-key>) CRV X Y
     All fields are strings, base64 encoding the parameters, except CRV, which is a symbol.

 -- Class: <jwks> () KEYS
     An identity provider may use different keys that are in validity to sign different access tokens. The JWKS encapsulates many public KEYS.

 -- Generic method: <public-key> public-key (KEY <key-pair>)
 -- Generic method: <public-key> public-key (KEY <public-key>)
     Return the public part of KEY, which may either be a key pair or a public key.

 -- Generic method: <private-key> private-key (KEY <key-pair>)
 -- Generic method: <private-key> private-key (KEY <private-key>)
     Return the private part of KEY.

 -- Generic method: <string> rsa-d (KEY <rsa-key-pair>)
 -- Generic method: <string> rsa-d (KEY <rsa-private-key>)
 -- Generic method: <string> rsa-p (KEY <rsa-key-pair>)
 -- Generic method: <string> rsa-p (KEY <rsa-private-key>)
 -- Generic method: <string> rsa-q (KEY <rsa-key-pair>)
 -- Generic method: <string> rsa-q (KEY <rsa-private-key>)
 -- Generic method: <string> rsa-dp (KEY <rsa-key-pair>)
 -- Generic method: <string> rsa-dp (KEY <rsa-private-key>)
 -- Generic method: <string> rsa-dq (KEY <rsa-key-pair>)
 -- Generic method: <string> rsa-dq (KEY <rsa-private-key>)
 -- Generic method: <string> rsa-qi (KEY <rsa-key-pair>)
 -- Generic method: <string> rsa-qi (KEY <rsa-private-key>)
 -- Generic method: <string> rsa-n (KEY <rsa-key-pair>)
 -- Generic method: <string> rsa-n (KEY <rsa-public-key>)
 -- Generic method: <string> rsa-e (KEY <rsa-key-pair>)
 -- Generic method: <string> rsa-e (KEY <rsa-public-key>)
 -- Generic method: <symbol> ec-crv (KEY <ec-key-pair>)
 -- Generic method: <symbol> ec-crv (KEY <ec-point>)
 -- Generic method: <symbol> ec-crv (KEY <ec-scalar>)
 -- Generic method: <string> ec-x (KEY <ec-key-pair>)
 -- Generic method: <string> ec-x (KEY <ec-point>)
 -- Generic method: <string> ec-y (KEY <ec-key-pair>)
 -- Generic method: <string> ec-y (KEY <ec-point>)
 -- Generic method: <string> ec-z (KEY <ec-key-pair>)
 -- Generic method: <string> ec-z (KEY <ec-scalar>)
     Key parameter getters.

 -- Generic method: <list> keys (JWKS <jwks>)
     Return all the public keys used by JWKS.

 -- Generic method: <undefined> check-key (KEY <key>)
 -- Generic method: <undefined> check-key (KEY <key-pair>)
     Check that the KEY parameters are consistent.

When exchanging keys, maybe you will have them in the form of a JWK: an alist from symbols to strings, as a representation for a JSON object.

 -- Generic method: <list> key->jwk (KEY <key>)
 -- Generic method: <list> key->jwk (KEY <key-pair>)
     Return an alist with known parameter names for JSON.

 -- function: jwk->key JWK
     Parse JWK as a key or a key pair.

 -- Generic method: <symbol> kty (KEY <rsa-key-pair>)
 -- Generic method: <symbol> kty (KEY <rsa-public-key>)
 -- Generic method: <symbol> kty (KEY <rsa-private-key>)
 -- Generic method: <symbol> kty (KEY <ec-key-pair>)
 -- Generic method: <symbol> kty (KEY <ec-point>)
 -- Generic method: <symbol> kty (KEY <ec-scalar>)
     Return 'RSA for RSA keys, or 'EC for elliptic curve keys.

 -- Generic method: <string> jkt (KEY <key-pair>)
 -- Generic method: <string> jkt (KEY <public-key>)
     Hash the KEY parameters in a reproducible order to get the hash of a key.

 -- function: generate-key [#:N-SIZE] [#:E-SIZE] [#:E=\"AQAB\"] [#:CRV]
     Generate a new key pair.

 -- Generic method: <values> serve (JWKS <jwks>) EXPIRATION-DATE
     Return a response and response body for serving JWKS. Client-side caching is very much necessary for a JWKS, so pass EXPIRATION-DATE as a SRFI-19 date to define a maximum date for caching. It should be in the future, for instance in 1 hour.

 -- function: get-jwks URI [#:HTTP-REQUEST]
     Download a JWKS on the web at URI. Use HTTP-REQUEST, with the same interface as that of (web client), to actually get the JWKS.

 -- Exception type: &not-a-jwk
     If the key parameters are incorrect, this exception is raised.

 -- Exception type: &not-a-jwks
     If the JWKS cannot be downloaded, or is incorrect, this exception is raised.

Caching on server side
**********************

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.

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 XDG_CACHE_HOME. 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.

The (webid-oidc cache) module exports two functions to deal with the cache.

 -- function: clean-cache [#PERCENTS]
     Drop PERCENTS% of the cache right now.

 -- function: with-cache [#HTTP-GET]
     Return a function acting as http-get from (web client) (takes an URI as the first parameter, and an optional #:HEADERS set, and returns 2 values, the response and its body).

     The cache will be read and written in the web-cache subdirectory of the cache home. To check the time window validity, the CURRENT-DATE parameter is used.

     The back-end function, HTTP-GET, defaults to that of (web client).

 -- parameter: cache-home
     This parameters sets the cache directory. By default, it is XDG_CACHE_HOME.

Content negociation
*******************

There are a number of different available syntaxes for RDF, some being simple and human readable like turtle, and others more adapted to the JavaScript ecosystem like json-ld. To help clients both from and outside of the JS ecosystem, the server needs to perform content negociation, i.e. convert from one content-type to another.

 -- function from (webid-oidc serve): convert CLIENT-ACCEPTS SERVER-NAME PATH CONTENT-TYPE CONTENT
     Convert the resource representation under PATH on SERVER-NAME, which has a given CONTENT-TYPE and CONTENT, to a content-type that the CLIENT ACCEPTS.

     Return 2 values:

      1. the accepted content-type;

      2. the content in the given content-type.

     Currently, the only conversions are from and to Turtle and N-Quads.

Running an Identity Provider
****************************

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.

You can start it by invoking the webid-oidc program with the issuer command, with the following options:

-h, or --help
     prints a summary of options and exit.

-v, or --version
     prints the version of the program and exits.

-n URI, or --server-name=URI
     sets the global server name of the identity provider. It should have an empty path.

-k FILE.JWK, or --key-file=FILE.JWK
     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.

-s WEBID, or --subject=WEBID
     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.

-w PASSWORD, or --password=PASSWORD
     sets the password that the user must enter to authorize an application.

-j URI, or --jwks-uri=URI
     tells the server that requests to URI should be responded with the public key used to sign the tokens.

-a URI, or --authorization-endpoint-uri=URI
     tells the server that requests to URI should be treated as authorization requests.

-t URI, or --token-endpoint-uri=URI
     tells the server that requests to URI should be treated as token negociation requests.

-p PORT, or --port=PORT
     change the port number used by the server. By default, it is set to 8080.

-l FILE.LOG, or --log-file=FILE.LOG
     let the server dump all its output to FILE.LOG. Since I don’t know how to deal with syslog, this is the only way to keep logs with a shepherd service.

-e FILE.ERR, or --error-file=FILE.ERR
     let the server dump all its errors to FILE.ERR.

The program is sensitive to the environment variables. The most important one is LANG, 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.

The XDG_DATA_HOME should point to some place where the program will store refresh tokens, under the webid-oidc directory. For a system service, you might want to define that environment to /var/lib, for instance.

The XDG_CACHE_HOME should point to a directory where to store the seed of the random number generator (under a webid-oidc 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.

Running a Resource Server
*************************

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.

The authenticator
=================

In (webid-oidc resource-server), the following function gives a simple API for a web server:

 -- function: make-authenticator JTI-LIST [#SERVER-URI] [#CURRENT-TIME] [#HTTP-GET]
     Create an authenticator, i.e. a function that takes a request and request body and returns the webid of the authenticated user, or #f if it is not authenticated.

     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.

     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.

     The JTIs are checked within a small time frame. By default, the system time will be used. Otherwise, you can customize the current-time optional keyword argument, to pass a thunk returning a time from (srfi srfi-19).

     You may want to customize the HTTP-GET optional keyword argument to pass a function to replace http-get from (http client). This function takes an URI and optional #:headers arguments, makes the request, and return two values: the response, and the response body.

     This function, in (webid-oidc resource-server), 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.

The full server
===============

 -- function from (webid-oidc resource-server): make-server [#:SERVER-URI] [#:OWNER] [#:AUTHENTICATOR] [#:CURRENT-TIME] [#:HTTP-GET]
     Return a server handler, a function taking 2 values, a request and a request body, and returning 2 values, the response and response body.

     The optional [#:AUTHENTICATOR] argument defaults to the webid-oidc authenticator, [#:CURRENT-TIME] defaults to a thunk returning the system time and [#:HTTP-GET] to the web client from (web client).

Resources stored on the server
==============================

To store and serve resources, the server has two distinct mechanisms. A content is a read-only possible value for a resource, indexed by etags, and a path is a mutable value that indicates the etag of the resource, and of the auxiliary resources (description and ACL). With this separation, it is possible to atomically delete a resource and all associated auxiliary resources, by unlinking the corresponding path. It is also possible to mutate separately the ACL and the resource itself without writing a copy for both.

The content API is contained in the (webid-oidc server resource content) module.

 -- function: with-session F
     Call F with 5 arguments:

       * a function to get the content-type of a given etag;

       * a function to list the paths contained within the resource;

       * a function to load the content of a given etag;

       * a function to create a new content;

       * a function to remove a content from the file system. It is still possible to query it with the first 3 functions, but new sessions will not see it.

     Since the contents are read-only, it is possible to cache the value of the content in memory. This is why F should run within a session with memoization.

     Resources only store static content, because the membership triples for containers is considered dynamic and not included in the representation.

     The first 3 functions as well as the last one are called with an etag, and the function to create a content is called with the content-type, list of contained paths, and (static) content.

     The contents are searched in the server/content subdirectory of DATA-HOME.

 -- parameter: data-home
     Defines the directory where to store persistent data. Defaults to XDG_DATA_HOME.

The path API is defined in (webid-oidc server resource path).

 -- function: read-path PATH
     Read the resource at PATH, and return 2 values:

      1. the ETag of the main resource;

      2. an alist where keys are auxiliary resource type URIs (the type is from (web uri)), and the values are ETags of the corresponding resource.

     If the resource is not found, raise an exception with type &path-not-found, and maybe &uri-slash-semantics-error if a resource with a different ending-in-slash exists.

     This function is safe to call when the path is being modified, either by another thread, process or else, as the returned values will always be consistent. However, once the function returns, an updating process may have deleted the returned ETags. If this is the case, then you must call this function again to read the updated path.

 -- function: update-path PATH F CONTENT-TYPE CONTAINED STATIC-CONTENT CREATE DELETE [#:CREATE-INTERMEDIATE-CONTAINERS?=#f]
     Read PATH, call F with two values: the ETag and the auxiliary ETags (as returned by READ-PATH), and update the path accordingly. If PATH does not exist, then the first argument is #f and the second one is the empty list.

     If F returns #f, then the resource is deleted.

     If F returns an ETag as the first returned value and an alist of auxiliary resource ETags as the second value, then the resource is updated.

     The last functions are from the content API. Since creating or deleting children requires updating the parent, we need them.

     Some operations should create the intermediate containers for a given path, this is the case for the PUT HTTP verb. For POST, the parent should exist. The #:CREATE-INTERMEDIATE-CONTAINERS? switch lets you change the behavior. In any case, it is an error to delete a non-empty container.

     The update is atomic, meaning that at any point in time the file is fully written out. Concurrent access to the same resource is performed by locking the lock file named X/.lock, where X is the first character of the base64-url sha-256 hash of the path. The lock file is not meant to be removed when the resource is unlocked. It should be locked with flock instead. Like other forms of lock-based synchronization, this function is not composable. This means that you cannot call this function within F, otherwise a deadlock may ensue.

     If the resource is created or deleted, then the parent resource is updated as well. To avoid deadlocks with other processes, please follow the following rules: lock the path, then lock the parent path, then update the parent, then unlock the parent, and finally unlock the child path.

The Web Access Control specification defines an RDF vocabulary to check whether a given user is allowed to perform some operations. The (webid-oidc server resource wac) helps you do that.

 -- function: wac-get-modes SERVER-NAME PATH USER [#:HTTP-GET]
     Return the list of modes that are allowed for USER accessing PATH. The SERVER-NAME URI is required to find the relevant triples in the ACL. If USER is unauthenticated, pass #f.

     Please note that in any case, the data owner should have all rights whatsoever, bypassing WAC. Otherwise, it is possible to steal control away from the data owner.

 -- function: check-acl-can-read SERVER-NAME PATH OWNER USER [#:HTTP-GET]
 -- function: check-acl-can-write SERVER-NAME PATH OWNER USER [#:HTTP-GET]
 -- function: check-acl-can-append SERVER-NAME PATH OWNER USER [#:HTTP-GET]
 -- function: check-acl-can-control SERVER-NAME PATH OWNER USER [#:HTTP-GET]
     Assert that the resource at PATH on SERVER-NAME is owned by OWNER, and check that USER has the proper authorization. Otherwise, raise an exception of type &forbidden.

Running a client
****************

The job of the client is to use accounts to fetch private resources on the web. The (webid-oidc client) defines the <client> class.

 -- Class: <client> CLIENT-ID KEY-PAIR REDIRECT-URI
     In OIDC, a client is an application that does not hold the resources. It may in fact be a network server available on the web, or a program that you run on your machine. Being a network server or not is irrelevant.

     The <client> class is designed with immutability in mind. You can create a client with the make generic method, using these keywords to initialize values:

     #:client-id
          to set the public client identifier (this endpoint should be available on the world-wide web), as a string representing an URI or an URI from (web uri);

     #:key-pair
          to use a specific key pair. If not set, a new key pair will be generated;

     #:redirect-uri
          to set the redirect URI that the application controls. It may just be a page showing the authorization code, with instructions on how to paste this code into the application. It should match one of the authorized redirect URIs in the client identifier endpoint.

          If you want to set a state parameter for the redirection, you can do it by setting the guile parameter authorization-state.

 -- Generic method: uri client-id (CLIENT <client>)
 -- Generic method: key pair client-key-pair (CLIENT <client>)
 -- Generic method: uri client-redirect-uri (CLIENT <client>)
     Slot accessors for CLIENT.

 -- Parameter: client
     Define this parameter to set the client to use to access private data.

To access private data, you must identify yourself. The (webid-oidc client accounts) module lets you define accounts.

 -- Class: <account> SUBJECT ISSUER ID-TOKEN ACCESS-TOKEN REFRESH-TOKEN KEY-PAIR
     Encapsulate an account. SUBJECT is your webid, while ISSUER is a host name. ID-TOKEN is the decoded OIDC ID token, i.e. a pair of (header . payload), because we don’t need to show it to any other party, so its authenticity needs not be demonstrated. However, ACCESS-TOKEN is an encoded access token (into a string), because we don’t need to worry about its internals on client side.

     There are different ways to initialize an account. First, you can save all parameters to some form of storage, and restore it by using the associated keyword arguments at construction time:

     #:subject

     #:issuer

     #:id-token

     #:access-token

     #:refresh-token

     #:key-pair

     If you want to make a new account, you would ask the user for an identity provider, and pass it with #:issuer as the only initialized value. The constructor will log you in, using the authorization-process and anonymous-http-request function parameters.

     If you want to refresh an access token, you would also set #:refresh-token.

     In any case, when you don’t specify a value, it’s as if you passed #f.

 -- Parameter: authorization-process
     This function is called when an explicit user authorization is required, for instance because there is no refresh token and the access token expired. The function takes an URI as argument, with an additional #:issuer keyword argument containing the issuer. In this function, you should ask the user to browse this URI so that your application gets the authorization code.

 -- Parameter: anonymous-http-request
     This function is used as a back-end for private resource access, and to query the server configuration. It defaults to http-request from (web client).

 -- Generic method: uri subject (ACCOUNT <account>)
 -- Generic method: <account> set-subject (ACCOUNT <account>) (URI string or URI)
 -- Generic method: uri issuer (ACCOUNT <account>)
 -- Generic method: <account> set-issuer (ACCOUNT <account>) (URI string or URI)
 -- Generic method: optional decoded ID token id-token (ACCOUNT <account>)
 -- Generic method: <account> set-id-token (ACCOUNT <account>) (ID-TOKEN optional ID token)
 -- Generic method: optional encoded access token access-token (ACCOUNT <account>)
 -- Generic method: <account> set-access-token (ACCOUNT <account>) (ACCESS-TOKEN optional access token)
 -- Generic method: optional <string> refresh-token (ACCOUNT <account>)
 -- Generic method: <account> set-refresh-token (ACCOUNT <account>) (REFRESH-TOKEN optional <string>)
 -- Generic method: key pair key-pair (ACCOUNT <account>)
 -- Generic method: <account> set-key-pair (ACCOUNT <account>) (KEY-PAIR optional key pair)
     Slot accessors and functional setters for ACCOUNT.

If you intend to run a public network server as a client application, you may have multiple different users, but you should not let any user use any account. If this is the case, you can either store the accounts on the user agent storage (for instance, as a cookie), or store all of them on the server. If you choose to store the accounts on the user agent, at least use a new key pair for each of them. If you want to store the user database on the server side, be aware that no entity other than yourself will check that your user abides by any term of service, so it is possible that a single user makes a lot of accounts to annoy you and fill your hard drive with key pairs. If your application does not let random people to use it, you might want to use protected accounts, to help you check that the users cannot impersonate each other.

 -- Class: <protected-account> (<account>) USERNAME ENCRYPTED-PASSWORD
     This superclass of <account> is protected by a username and password. It is constructed with the initializer keywords #:username and #:encrypted-password.

 -- Generic method: <string> username (PROTECTED-ACCOUNT <protected-account>)
 -- Generic method: <protected-account> set-username (PROTECTED-ACCOUNT <protected-account>) (USERNAME <string>)
 -- Generic method: <string> encrypted-password (PROTECTED-ACCOUNT <protected-account>)
 -- Generic method: <protected-account> set-encrypted-password (PROTECTED-ACCOUNT <protected-account>) (ENCRYPTED-PASSWORD <string>)
     Slot accessors and functional setters for PROTECTED-ACCOUNT.

 -- Generic method: <account> invalidate-access-token (ACCOUNT <account>)
     Indicate that the access token in ACCOUNT cannot be used. Before using ACCOUNT again, you will need to refresh the access token. This function does not mutate ACCOUNT.

 -- Generic method: <account> invalidate-refresh-token (ACCOUNT <account>)
     Indicate that the refresh token has been revoked for ACCOUNT. This is usually an indication that the user don’t want your application to access her private data.  This function does not mutate ACCOUNT.

 -- Generic method: <account> refresh (ACCOUNT <account>)
     Refresh the access token.

 -- Exception type: &authorization-code-required URI
     If the login process requires the user to send an authorization code, an exception of this type will be raised, with an implicit invitation for the user to browse URI and follow the instructions.

     The instructions will be handled by the REDIRECT-URI in the login function. If your client is a traditional web application, the user will be redirected to this URI with an authorization code. If your client is a native application, then maybe that redirection URI should display the authorization code and invite the user to paste it in the appropriate place in the application.

     When an exception of this type is raised during the login function, it is continuable, meaning that the login function will resume. You need to create an exception handler for an exception of this type, look up the URI, direct the user to browse it, get the authorization code back, and return the authorization code from the exception handler.

 -- function: make-authorization-code-required URI
 -- function: authorization-code-required? ERROR
 -- function: authorization-code-required-uri ERROR
     Constructor, predicate, and accessor for the &authorization-code-required exception type.

 -- Exception type: &refresh-token-expired
     The refresh token can be used to still perform requests on behalf of the user when perse is offline. However, if the refresh token expires while the user is offline, it is not possible to log in again, because it requires a new authorization code. So, it is not possible to recover from this error, and the refresh token is immediately discarded.

 -- function: make-refresh-token-expired
 -- function: refresh-token-expired? ERROR
     Constructor and predicate for the &refresh-token-expired exception type.

 -- function: invalidate-access-token ACCOUNT
     Discard the access token for ACCOUNT. It is not saved in the user database yet. This is roughly equivalent to log out.

 -- function: invalidate-refresh-token ACCOUNT
     Discard the refresh token for ACCOUNT. You still need to save the ACCOUNT.

 -- Exception type: &token-request-failed RESPONSE RESPONSE-BODY
     If the token endpoint is unable to deliver an identity token and an access token, this exception is raised with the identity provider RESPONSE and RESPONSE BODY. This exception cannot be continued.

 -- function: make-token-request-failed RESPONSE RESPONSE-BODY
 -- function: token-request-failed? ERROR
 -- function: token-request-response ERROR
 -- function: token-request-response-body ERROR
     Constructor, predicate, and accessors for the &token-request-failed exception type.

The (webid-oidc client) module provides the most useful function for a client.

 -- function: request ACCOUNT URI . ARGS
     Perform a request on behalf of ACCOUNT, with the current value of the CLIENT parameter as the client, using as a backend the current value of ANONYMOUS-HTTP-REQUEST.

Finally, to implement your application, there needs to be a public endpoint for the resource server to check that you are not impersonating another application. This endpoint can be served by any web server, but a convenience procedure is made available here:

 -- function: serve-application ID REDIRECT-URI [#CLIENT-NAME] [#CLIENT-URI]
     Return a handler for web requests to serve the application manifest and the redirection to transmit the authorization code. You should set the CLIENT-NAME to your application name and CLIENT-URI to point to where to a presentation of your application.

Exceptional conditions
**********************

The library will raise an exception whenever something fishy occurs. For instance, if a signature is invalid, or the expiration date has passed.

When the client is responsible for an error, such as presenting an invalid access token, a compound exception is raised. It is sometimes useful for the user to understand what happened, because it could indicate a problem in a part of the web they need to change. For instance, if the access token cannot be decoded because the identity provider is down, then maybe informing the user of that fact is useful.

However, presenting too much information is a security risk. For instance, if the system administrator also runs a private server on the same machine, and a malicious client tries to pretend that this private server is an identity provider, then the public server will try to query the private server. If an error happens and the public server displays some information to the client, then a part of the information comes from the private server. Thus, a balance needs to be found so that not too much is revealed.

The module (webid-oidc errors) defines an exception type that indicates a message that is safe to display to the user.

 -- Exception type: &message-for-the-user MESSAGE
     Indicate that MESSAGE can be safely displayed to the user. It is an XHTML paragraph (or equivalent), presented as SXML.

 -- function: make-message-for-the-user MESSAGE
 -- user-message: EXCEPTION
     Constructor and accessor for the &message-for-the-user exception type.

GNU Free Documentation License
******************************

     [file fdl.texi not included]