server: add an exception for showing a message to the user

7 files changed, 289 insertions, 155 deletions

diff --git a/doc/disfluid.texi b/doc/disfluid.texi
index fa5347a..6b9ad08 100644
--- a/doc/disfluid.texi
+++ b/doc/disfluid.texi
@@ -1539,10 +1539,80 @@ Return the path prefix @var{endpoint} is configured to respond to.
 Check if @var{endpoint} is configured to respond to @var{request}.
 @end deffn
 
+The handler may throw exceptions to signal errors. Exception messages
+will be printed to the log file, and user messages will be passed to
+the user.
+
 @menu
+* Error signalling::
 * Router endpoint::
 @end menu
 
+@node Error signalling
+@section Error signalling
+The @emph{(webid-oidc server endpoint)} module defines exception types
+that can be emitted to abort the computation in a handler. If an
+exception of a different kind is raised, this will lead to a 500
+Internal Server Error response.
+
+@deftp {Exception type} &web-exception @var{code} @var{reason-phrase}
+The request failed, with @var{code} and @var{reason-phrase}.
+@end deftp
+
+@deffn {function} make-web-exception @var{code} @var{reason-phrase}
+Create an exception with @var{code} and @var{reason-phrase}.
+@end deffn
+
+@deffn {function} web-exception? @var{exn}
+Check if @var{exn} was thrown because the request failed.
+@end deffn
+
+@deffn {function} web-exception-code @var{exn}
+@deffnx {function} web-exception-reason-phrase @var{exn}
+Return the code and reason-phrase for when @var{exn} was thrown, if it
+was thrown because of a failing request.
+@end deffn
+
+@deftp {Exception type} &caused-by-user @var{webid}
+If a web exception is raised, maybe it is caused by some user
+identified by @var{webid} (an URI, or @code{#f}.
+@end deftp
+
+@deffn {function} make-caused-by-user @var{webid}
+Constructor for @code{&caused-by-user}.
+@end deffn
+
+@deffn {function} caused-by-user? @var{exn}
+Check if @var{exn} was caused by the user.
+@end deffn
+
+@deffn {function} caused-by-user-webid @var{exn}
+Return the webid of the user that caused @var{exn}.
+@end deffn
+
+@deftp {Exception type} &user-message @var{sxml}
+An exception containing a message that is safe to show to the user, as
+an SXML fragment of XHTML. Typically, this would be a @code{<p/>}, or
+a @code{<div/>}.
+
+You can set a user-message multiple times. The occurences will be
+concatenated in the response, in the order they appear in the
+composite exception.
+@end deftp
+
+@deffn {function} make-user-message @var{sxml}
+Create a new user message containing the @var{sxml} fragment.
+@end deffn
+
+@deffn {function} user-message? @var{exn}
+Check if there is at least one user message in @var{exn}.
+@end deffn
+
+@deffn {function} user-message-sxml @var{exn}
+Return all user messages in @var{exn}, as a @code{<div/>} SXML
+fragment.
+@end deffn
+
 @node Router endpoint
 @section Router endpoint
 The first non-trivial handler is for the router endpoint, defined in
diff --git a/po/disfluid.pot b/po/disfluid.pot
index 6468cb0..c4468f3 100644
--- a/po/disfluid.pot
+++ b/po/disfluid.pot
@@ -8,7 +8,7 @@ msgid ""
 msgstr ""
 "Project-Id-Version: disfluid SNAPSHOT\n"
 "Report-Msgid-Bugs-To: vivien@planete-kraus.eu\n"
-"POT-Creation-Date: 2021-10-19 11:29+0200\n"
+"POT-Creation-Date: 2021-10-19 11:31+0200\n"
 "PO-Revision-Date: YEAR-MO-DA HO:MI+ZONE\n"
 "Last-Translator: FULL NAME <EMAIL@ADDRESS>\n"
 "Language-Team: LANGUAGE <LL@li.org>\n"
@@ -238,7 +238,7 @@ msgid "#:webid should be an URI"
 msgstr ""
 
 #: src/scm/webid-oidc/access-token.scm:122
-#: src/scm/webid-oidc/client-manifest.scm:212
+#: src/scm/webid-oidc/client-manifest.scm:223
 msgid "#:client-id should be an URI"
 msgstr ""
 
@@ -282,9 +282,9 @@ msgstr ""
 #: src/scm/webid-oidc/hello-world.scm:167
 #: src/scm/webid-oidc/hello-world.scm:187
 #: src/scm/webid-oidc/identity-provider.scm:136
-#: src/scm/webid-oidc/token-endpoint.scm:112
-#: src/scm/webid-oidc/token-endpoint.scm:138
-#: src/scm/webid-oidc/token-endpoint.scm:165
+#: src/scm/webid-oidc/token-endpoint.scm:113
+#: src/scm/webid-oidc/token-endpoint.scm:139
+#: src/scm/webid-oidc/token-endpoint.scm:166
 msgid "xml-lang|en"
 msgstr ""
 
@@ -319,8 +319,8 @@ msgid "Allow"
 msgstr ""
 
 #: src/scm/webid-oidc/authorization-page-unsafe.scm:95
-#: src/scm/webid-oidc/token-endpoint.scm:130
-#: src/scm/webid-oidc/token-endpoint.scm:157
+#: src/scm/webid-oidc/token-endpoint.scm:131
+#: src/scm/webid-oidc/token-endpoint.scm:158
 msgid "reason-phrase|Bad Request"
 msgstr ""
 
@@ -394,76 +394,76 @@ msgstr ""
 msgid "Unsupported delegate catalog URI scheme: ~s\n"
 msgstr ""
 
-#: src/scm/webid-oidc/client-manifest.scm:143
+#: src/scm/webid-oidc/client-manifest.scm:144
 #, scheme-format
 msgid "cannot fetch a client manifest: ~a"
 msgstr ""
 
-#: src/scm/webid-oidc/client-manifest.scm:145
+#: src/scm/webid-oidc/client-manifest.scm:146
 msgid "cannot fetch a client manifest"
 msgstr ""
 
-#: src/scm/webid-oidc/client-manifest.scm:154
+#: src/scm/webid-oidc/client-manifest.scm:155
 #, scheme-format
 msgid "the server responded with code ~a"
 msgstr ""
 
-#: src/scm/webid-oidc/client-manifest.scm:157
+#: src/scm/webid-oidc/client-manifest.scm:159
 #, scheme-format
-msgid "The server hosting your application responded with code ~a."
+msgid "<p>The server hosting your application responded with code ~a.<p>"
 msgstr ""
 
-#: src/scm/webid-oidc/client-manifest.scm:166
-#: src/scm/webid-oidc/client-manifest.scm:195
+#: src/scm/webid-oidc/client-manifest.scm:169
+#: src/scm/webid-oidc/client-manifest.scm:202
 msgid "the client manifest does not have a client_id field"
 msgstr ""
 
-#: src/scm/webid-oidc/client-manifest.scm:168
-#: src/scm/webid-oidc/client-manifest.scm:197
+#: src/scm/webid-oidc/client-manifest.scm:172
+#: src/scm/webid-oidc/client-manifest.scm:205
 msgid ""
-"The server hosting your application does not behave correctly, because it "
-"lacks the client_id field."
+"<p>The server hosting your application does not behave correctly, because it "
+"lacks the client_id field.<p>"
 msgstr ""
 
-#: src/scm/webid-oidc/client-manifest.scm:188
+#: src/scm/webid-oidc/client-manifest.scm:193
 msgid "the client manifest does not have a redirect_uris field"
 msgstr ""
 
-#: src/scm/webid-oidc/client-manifest.scm:190
+#: src/scm/webid-oidc/client-manifest.scm:196
 msgid ""
-"The server hosting your application does not behave correctly, because it "
-"lacks the redirect_uris field."
+"<p>The server hosting your application does not behave correctly, because it "
+"lacks the redirect_uris field.<p>"
 msgstr ""
 
-#: src/scm/webid-oidc/client-manifest.scm:203
+#: src/scm/webid-oidc/client-manifest.scm:212
 #, scheme-format
 msgid "the client manifest under ~s has a client_id of ~s"
 msgstr ""
 
-#: src/scm/webid-oidc/client-manifest.scm:207
+#: src/scm/webid-oidc/client-manifest.scm:217
 msgid ""
-"The application you want to use does not control the domain name it appears "
-"to represent."
+"<p>The application you want to use does not control the domain name it "
+"appears to represent.</p>"
 msgstr ""
 
-#: src/scm/webid-oidc/client-manifest.scm:221
+#: src/scm/webid-oidc/client-manifest.scm:232
 msgid "#:redirect-uris should be a list of URIs"
 msgstr ""
 
-#: src/scm/webid-oidc/client-manifest.scm:231
+#: src/scm/webid-oidc/client-manifest.scm:242
 #, scheme-format
 msgid "the client manifest does not allow ~s as a redirection uri"
 msgstr ""
 
-#: src/scm/webid-oidc/client-manifest.scm:235
+#: src/scm/webid-oidc/client-manifest.scm:246
 #, scheme-format
 msgid ""
 "<p>The application wants to get your\n"
-"authorization through <strong>~s</strong>, which is not\n"
+"authorization through <strong>~a</strong>, which is not\n"
 "approved.</p>"
 msgstr ""
 
-#: src/scm/webid-oidc/client-manifest.scm:270
+#: src/scm/webid-oidc/client-manifest.scm:283
 msgid "cannot serve the public manifest"
 msgstr ""
 
@@ -2168,7 +2168,7 @@ msgid "~a: ignoring a group that cannot be fetched\n"
 msgstr ""
 
 #: src/scm/webid-oidc/resource-server.scm:334
-#: src/scm/webid-oidc/token-endpoint.scm:104
+#: src/scm/webid-oidc/token-endpoint.scm:105
 msgid "reason-phrase|Forbidden"
 msgstr ""
 
@@ -2222,27 +2222,35 @@ msgstr ""
 msgid "cannot POST to an auxiliary resource path, ~s"
 msgstr ""
 
-#: src/scm/webid-oidc/server/endpoint.scm:65
+#: src/scm/webid-oidc/server/endpoint.scm:98
+msgid "No information available."
+msgstr ""
+
+#: src/scm/webid-oidc/server/endpoint.scm:119
 msgid "#:host should be a string or #f"
 msgstr ""
 
-#: src/scm/webid-oidc/server/endpoint.scm:70
+#: src/scm/webid-oidc/server/endpoint.scm:124
 msgid "#:path should be an absolute path"
 msgstr ""
 
-#: src/scm/webid-oidc/server/endpoint.scm:90
+#: src/scm/webid-oidc/server/endpoint.scm:144
 #, scheme-format
 msgid "#:routed element ~a should be an endpoint"
 msgstr ""
 
-#: src/scm/webid-oidc/server/endpoint.scm:95
+#: src/scm/webid-oidc/server/endpoint.scm:149
 msgid "#:routed should be a list of endpoints"
 msgstr ""
 
-#: src/scm/webid-oidc/server/endpoint.scm:128 src/ui/error-page.glade:73
+#: src/scm/webid-oidc/server/endpoint.scm:181 src/ui/error-page.glade:73
 msgid "Not Found"
 msgstr ""
 
+#: src/scm/webid-oidc/server/endpoint.scm:182
+msgid "The resource could not be found."
+msgstr ""
+
 #: src/scm/webid-oidc/server/read.scm:101
 #, scheme-format
 msgid "the auxiliary resource of type ~s at ~s is absent"
@@ -2296,46 +2304,46 @@ msgstr ""
 msgid "an error happened while updating file ~s"
 msgstr ""
 
-#: src/scm/webid-oidc/token-endpoint.scm:92
+#: src/scm/webid-oidc/token-endpoint.scm:93
 #, scheme-format
 msgid "while handling web failure for the token endpoint: ~a"
 msgstr ""
 
-#: src/scm/webid-oidc/token-endpoint.scm:94
+#: src/scm/webid-oidc/token-endpoint.scm:95
 msgid "an error happened during the token endpoint failure handling"
 msgstr ""
 
-#: src/scm/webid-oidc/token-endpoint.scm:224
+#: src/scm/webid-oidc/token-endpoint.scm:225
 msgid "missing grant type"
 msgstr ""
 
-#: src/scm/webid-oidc/token-endpoint.scm:228
+#: src/scm/webid-oidc/token-endpoint.scm:229
 msgid "<p>You did not specify a grant_type for this request.</p>"
 msgstr ""
 
-#: src/scm/webid-oidc/token-endpoint.scm:242
+#: src/scm/webid-oidc/token-endpoint.scm:243
 msgid "missing authorization code"
 msgstr ""
 
-#: src/scm/webid-oidc/token-endpoint.scm:246
+#: src/scm/webid-oidc/token-endpoint.scm:247
 msgid ""
 "<p>You want to grant an authorization code, but you did not set one.</p>"
 msgstr ""
 
-#: src/scm/webid-oidc/token-endpoint.scm:267
+#: src/scm/webid-oidc/token-endpoint.scm:268
 msgid "missing refresh token"
 msgstr ""
 
-#: src/scm/webid-oidc/token-endpoint.scm:271
+#: src/scm/webid-oidc/token-endpoint.scm:272
 msgid "<p>You want to grant a refresh token, but you did not set one.</p>"
 msgstr ""
 
-#: src/scm/webid-oidc/token-endpoint.scm:284
+#: src/scm/webid-oidc/token-endpoint.scm:285
 #, scheme-format
 msgid "unsupported grant type: ~s"
 msgstr ""
 
-#: src/scm/webid-oidc/token-endpoint.scm:289
+#: src/scm/webid-oidc/token-endpoint.scm:290
 #, scheme-format
 msgid ""
 "<p>You want to use <pre>~s</pre> as a grant type, but this is not supported."
diff --git a/po/fr.po b/po/fr.po
index 59df1e2..7479ac1 100644
--- a/po/fr.po
+++ b/po/fr.po
@@ -2,8 +2,8 @@ msgid ""
 msgstr ""
 "Project-Id-Version: webid-oidc 0.0.0\n"
 "Report-Msgid-Bugs-To: vivien@planete-kraus.eu\n"
-"POT-Creation-Date: 2021-10-19 11:29+0200\n"
-"PO-Revision-Date: 2021-10-18 13:25+0200\n"
+"POT-Creation-Date: 2021-10-19 11:31+0200\n"
+"PO-Revision-Date: 2021-10-19 11:31+0200\n"
 "Last-Translator: Vivien Kraus <vivien@planete-kraus.eu>\n"
 "Language-Team: French <vivien@planete-kraus.eu>\n"
 "Language: fr\n"
@@ -264,7 +264,7 @@ msgid "#:webid should be an URI"
 msgstr "#:webid doit être une URI"
 
 #: src/scm/webid-oidc/access-token.scm:122
-#: src/scm/webid-oidc/client-manifest.scm:212
+#: src/scm/webid-oidc/client-manifest.scm:223
 msgid "#:client-id should be an URI"
 msgstr "#:client-id doit être une URI"
 
@@ -313,9 +313,9 @@ msgstr ""
 #: src/scm/webid-oidc/hello-world.scm:167
 #: src/scm/webid-oidc/hello-world.scm:187
 #: src/scm/webid-oidc/identity-provider.scm:136
-#: src/scm/webid-oidc/token-endpoint.scm:112
-#: src/scm/webid-oidc/token-endpoint.scm:138
-#: src/scm/webid-oidc/token-endpoint.scm:165
+#: src/scm/webid-oidc/token-endpoint.scm:113
+#: src/scm/webid-oidc/token-endpoint.scm:139
+#: src/scm/webid-oidc/token-endpoint.scm:166
 msgid "xml-lang|en"
 msgstr "fr"
 
@@ -350,8 +350,8 @@ msgid "Allow"
 msgstr "Autoriser"
 
 #: src/scm/webid-oidc/authorization-page-unsafe.scm:95
-#: src/scm/webid-oidc/token-endpoint.scm:130
-#: src/scm/webid-oidc/token-endpoint.scm:157
+#: src/scm/webid-oidc/token-endpoint.scm:131
+#: src/scm/webid-oidc/token-endpoint.scm:158
 msgid "reason-phrase|Bad Request"
 msgstr "Requête Invalide"
 
@@ -428,84 +428,85 @@ msgstr "URI relative invalide"
 msgid "Unsupported delegate catalog URI scheme: ~s\n"
 msgstr "Schéma d’URI pour un catalogue délégé non supporté : ~s\n"
 
-#: src/scm/webid-oidc/client-manifest.scm:143
+#: src/scm/webid-oidc/client-manifest.scm:144
 #, scheme-format
 msgid "cannot fetch a client manifest: ~a"
 msgstr "impossible de télécharger un manifeste client : ~a"
 
-#: src/scm/webid-oidc/client-manifest.scm:145
+#: src/scm/webid-oidc/client-manifest.scm:146
 msgid "cannot fetch a client manifest"
 msgstr "impossible de télécharger un manifeste client"
 
-#: src/scm/webid-oidc/client-manifest.scm:154
+#: src/scm/webid-oidc/client-manifest.scm:155
 #, scheme-format
 msgid "the server responded with code ~a"
 msgstr "le serveur a répondu avec le code ~a"
 
-#: src/scm/webid-oidc/client-manifest.scm:157
+#: src/scm/webid-oidc/client-manifest.scm:159
 #, scheme-format
-msgid "The server hosting your application responded with code ~a."
-msgstr "Le serveur hébergeant votre application a répondu avec le code ~a."
+msgid "<p>The server hosting your application responded with code ~a.<p>"
+msgstr ""
+"<p>Le serveur hébergeant votre application a répondu avec le code ~a.</p>"
 
-#: src/scm/webid-oidc/client-manifest.scm:166
-#: src/scm/webid-oidc/client-manifest.scm:195
+#: src/scm/webid-oidc/client-manifest.scm:169
+#: src/scm/webid-oidc/client-manifest.scm:202
 msgid "the client manifest does not have a client_id field"
 msgstr "le manifeste client n’a pas de champ client_id"
 
-#: src/scm/webid-oidc/client-manifest.scm:168
-#: src/scm/webid-oidc/client-manifest.scm:197
+#: src/scm/webid-oidc/client-manifest.scm:172
+#: src/scm/webid-oidc/client-manifest.scm:205
 msgid ""
-"The server hosting your application does not behave correctly, because it "
-"lacks the client_id field."
+"<p>The server hosting your application does not behave correctly, because it "
+"lacks the client_id field.<p>"
 msgstr ""
-"Le serveur hébergeant votre application ne se comporte pas correctement, "
-"parce qu’il lui manque le champ client_id."
+"<p>Le serveur hébergeant votre application ne se comporte pas correctement, "
+"parce qu’il lui manque le champ client_id.</p>"
 
-#: src/scm/webid-oidc/client-manifest.scm:188
+#: src/scm/webid-oidc/client-manifest.scm:193
 msgid "the client manifest does not have a redirect_uris field"
 msgstr "le manifeste client n’a pas de champ redirect_uris"
 
-#: src/scm/webid-oidc/client-manifest.scm:190
+#: src/scm/webid-oidc/client-manifest.scm:196
 msgid ""
-"The server hosting your application does not behave correctly, because it "
-"lacks the redirect_uris field."
+"<p>The server hosting your application does not behave correctly, because it "
+"lacks the redirect_uris field.<p>"
 msgstr ""
-"Le serveur hébergeant votre application ne se comporte pas correctement, "
-"parce qu’il lui manque le champ redirect_uris."
+"<p>Le serveur hébergeant votre application ne se comporte pas correctement, "
+"parce qu’il lui manque le champ redirect_uris.</p>"
 
-#: src/scm/webid-oidc/client-manifest.scm:203
+#: src/scm/webid-oidc/client-manifest.scm:212
 #, scheme-format
 msgid "the client manifest under ~s has a client_id of ~s"
 msgstr "le manifeste client à ~s a un client_id valant ~s"
 
-#: src/scm/webid-oidc/client-manifest.scm:207
+#: src/scm/webid-oidc/client-manifest.scm:217
 msgid ""
-"The application you want to use does not control the domain name it appears "
-"to represent."
+"<p>The application you want to use does not control the domain name it "
+"appears to represent.</p>"
 msgstr ""
-"L’application que vous voulez utiliser ne contrôle pas le nom de domaine "
-"qu’elle prétend représenter."
+"<p>L’application que vous voulez utiliser ne contrôle pas le nom de domaine "
+"qu’elle prétend représenter.</p>"
 
-#: src/scm/webid-oidc/client-manifest.scm:221
+#: src/scm/webid-oidc/client-manifest.scm:232
 msgid "#:redirect-uris should be a list of URIs"
 msgstr "#:redirect-uris doit être une liste d’URIs"
 
-#: src/scm/webid-oidc/client-manifest.scm:231
+#: src/scm/webid-oidc/client-manifest.scm:242
 #, scheme-format
 msgid "the client manifest does not allow ~s as a redirection uri"
 msgstr "le manifeste client n’autorise pas ~s comme URI de redirection"
 
-#: src/scm/webid-oidc/client-manifest.scm:235
+#: src/scm/webid-oidc/client-manifest.scm:246
 #, scheme-format
 msgid ""
 "<p>The application wants to get your\n"
-"authorization through <strong>~s</strong>, which is not\n"
+"authorization through <strong>~a</strong>, which is not\n"
 "approved.</p>"
 msgstr ""
-"<p>L’applicationn veut récupérer votre code d’autorisation via <strong>~s</"
+"<p>L’applicationn veut récupérer votre code d’autorisation via <strong>~a</"
 "strong>, qui n’est pas approuvé.</p>"
 
-#: src/scm/webid-oidc/client-manifest.scm:270
+#: src/scm/webid-oidc/client-manifest.scm:283
 msgid "cannot serve the public manifest"
 msgstr "impossible de servir le manifeste public"
 
@@ -2562,7 +2563,7 @@ msgid "~a: ignoring a group that cannot be fetched\n"
 msgstr "~a : j’ignore un groupe qui ne peut pas être téléchargé\n"
 
 #: src/scm/webid-oidc/resource-server.scm:334
-#: src/scm/webid-oidc/token-endpoint.scm:104
+#: src/scm/webid-oidc/token-endpoint.scm:105
 msgid "reason-phrase|Forbidden"
 msgstr "Interdit"
 
@@ -2618,27 +2619,35 @@ msgstr "la ressource créée ne peut pas avoir de triplets de contention"
 msgid "cannot POST to an auxiliary resource path, ~s"
 msgstr "impossible de POSTer vers un chemin de ressource auxiliaire, ~s"
 
-#: src/scm/webid-oidc/server/endpoint.scm:65
+#: src/scm/webid-oidc/server/endpoint.scm:98
+msgid "No information available."
+msgstr "Pas d’information disponible."
+
+#: src/scm/webid-oidc/server/endpoint.scm:119
 msgid "#:host should be a string or #f"
 msgstr "#:host doit être une chaîne de caractères ou #f"
 
-#: src/scm/webid-oidc/server/endpoint.scm:70
+#: src/scm/webid-oidc/server/endpoint.scm:124
 msgid "#:path should be an absolute path"
 msgstr "#:path doit être un chemin URI absolu"
 
-#: src/scm/webid-oidc/server/endpoint.scm:90
+#: src/scm/webid-oidc/server/endpoint.scm:144
 #, scheme-format
 msgid "#:routed element ~a should be an endpoint"
 msgstr "élément #:routed ~a doit être un terminal"
 
-#: src/scm/webid-oidc/server/endpoint.scm:95
+#: src/scm/webid-oidc/server/endpoint.scm:149
 msgid "#:routed should be a list of endpoints"
 msgstr "#:routed doit être une liste de terminaux"
 
-#: src/scm/webid-oidc/server/endpoint.scm:128 src/ui/error-page.glade:73
+#: src/scm/webid-oidc/server/endpoint.scm:181 src/ui/error-page.glade:73
 msgid "Not Found"
 msgstr "Non Trouvé"
 
+#: src/scm/webid-oidc/server/endpoint.scm:182
+msgid "The resource could not be found."
+msgstr "La ressource n’a pas été trouvée."
+
 #: src/scm/webid-oidc/server/read.scm:101
 #, scheme-format
 msgid "the auxiliary resource of type ~s at ~s is absent"
@@ -2692,51 +2701,51 @@ msgstr "pendant la mise à jour du fichier ~s : ~a"
 msgid "an error happened while updating file ~s"
 msgstr "une erreur est survenue pendant la mise à jour du fichier ~s"
 
-#: src/scm/webid-oidc/token-endpoint.scm:92
+#: src/scm/webid-oidc/token-endpoint.scm:93
 #, scheme-format
 msgid "while handling web failure for the token endpoint: ~a"
 msgstr "lors de la gestion d’un échec web pour le terminal de jeton : ~a"
 
-#: src/scm/webid-oidc/token-endpoint.scm:94
+#: src/scm/webid-oidc/token-endpoint.scm:95
 msgid "an error happened during the token endpoint failure handling"
 msgstr ""
 "une erreur est survenue pendant la gestion d’un échec du terminal de jeton"
 
-#: src/scm/webid-oidc/token-endpoint.scm:224
+#: src/scm/webid-oidc/token-endpoint.scm:225
 msgid "missing grant type"
 msgstr "type d’offre manquant"
 
-#: src/scm/webid-oidc/token-endpoint.scm:228
+#: src/scm/webid-oidc/token-endpoint.scm:229
 msgid "<p>You did not specify a grant_type for this request.</p>"
 msgstr "<p>Vous n’avez pas spécifié de grant_type pour cette requête.</p>"
 
-#: src/scm/webid-oidc/token-endpoint.scm:242
+#: src/scm/webid-oidc/token-endpoint.scm:243
 msgid "missing authorization code"
 msgstr "code d’autorisation manquant"
 
-#: src/scm/webid-oidc/token-endpoint.scm:246
+#: src/scm/webid-oidc/token-endpoint.scm:247
 msgid ""
 "<p>You want to grant an authorization code, but you did not set one.</p>"
 msgstr ""
 "<p>Vous voulez offrir un code d’autorisation, mais vous n’en avez pas défini."
 "</p>"
 
-#: src/scm/webid-oidc/token-endpoint.scm:267
+#: src/scm/webid-oidc/token-endpoint.scm:268
 msgid "missing refresh token"
 msgstr "jeton de rafraîchissement manquant"
 
-#: src/scm/webid-oidc/token-endpoint.scm:271
+#: src/scm/webid-oidc/token-endpoint.scm:272
 msgid "<p>You want to grant a refresh token, but you did not set one.</p>"
 msgstr ""
 "<p>Vous voulez offrir un jeton de rafraîchissement, mais vous n’en avez pas "
 "défini.</p>"
 
-#: src/scm/webid-oidc/token-endpoint.scm:284
+#: src/scm/webid-oidc/token-endpoint.scm:285
 #, scheme-format
 msgid "unsupported grant type: ~s"
 msgstr "type d’offre non supporté : ~s"
 
-#: src/scm/webid-oidc/token-endpoint.scm:289
+#: src/scm/webid-oidc/token-endpoint.scm:290
 #, scheme-format
 msgid ""
 "<p>You want to use <pre>~s</pre> as a grant type, but this is not supported."
@@ -4559,10 +4568,6 @@ msgstr "Rejeter les modifications"
 #~ "--uri-sortant.\n"
 
 #, scheme-format
-#~ msgid "the resource ~s could not be found (because ~a)"
-#~ msgstr "la ressource ~s n’a pas été trouvée (parce que ~a)"
-
-#, scheme-format
 #~ msgid "the resource is missing an etag (see ~s)"
 #~ msgstr "la ressource n’a pas d’etag (voir ~s)"
 
diff --git a/src/scm/webid-oidc/client-manifest.scm b/src/scm/webid-oidc/client-manifest.scm
index 1d855c1..2d1f428 100644
--- a/src/scm/webid-oidc/client-manifest.scm
+++ b/src/scm/webid-oidc/client-manifest.scm
@@ -16,6 +16,7 @@
 
 (define-module (webid-oidc client-manifest)
   #:use-module (webid-oidc errors)
+  #:use-module (webid-oidc server endpoint)
   #:use-module (webid-oidc fetch)
   #:use-module (webid-oidc web-i18n)
   #:use-module (webid-oidc serializable)
@@ -153,9 +154,11 @@
                  (make-exception-with-message
                   (format #f (G_ "the server responded with code ~a")
                           (response-code response)))
-                 (make-message-for-the-user
-                  `(p ,(format #f (W_ "The server hosting your application responded with code ~a.")
-                               (response-code response)))))))
+                 (make-user-message
+                  (call-with-input-string
+                      (format #f (W_ "<p>The server hosting your application responded with code ~a.<p>")
+                              (response-code response))
+                    xml->sxml)))))
              (let ((json-data (stubs:json-string->scm response-body)))
                (let ((new-client-id (assq-ref json-data 'client_id))
                      (redirect-uris (assq-ref json-data 'redirect_uris)))
@@ -164,8 +167,10 @@
                     (make-exception
                      (make-exception-with-message
                       (G_ "the client manifest does not have a client_id field"))
-                     (make-message-for-the-user
-                      `(p ,(W_ "The server hosting your application does not behave correctly, because it lacks the client_id field."))))))
+                     (make-user-message
+                      (call-with-input-string
+                          (format #f (W_ "<p>The server hosting your application does not behave correctly, because it lacks the client_id field.<p>"))
+                        xml->sxml)))))
                  (set! redirect-uris
                        (let fix-redirect-uris ((redirect-uris redirect-uris))
                          (match redirect-uris
@@ -186,15 +191,19 @@
                     (make-exception
                      (make-exception-with-message
                       (G_ "the client manifest does not have a redirect_uris field"))
-                     (make-message-for-the-user
-                      `(p ,(W_ "The server hosting your application does not behave correctly, because it lacks the redirect_uris field."))))))
+                     (make-user-message
+                      (call-with-input-string
+                          (format #f (W_ "<p>The server hosting your application does not behave correctly, because it lacks the redirect_uris field.<p>"))
+                        xml->sxml)))))
                  (unless new-client-id
                    (raise-exception
                     (make-exception
                      (make-exception-with-message
                       (G_ "the client manifest does not have a client_id field"))
-                     (make-message-for-the-user
-                      `(p ,(W_ "The server hosting your application does not behave correctly, because it lacks the client_id field."))))))
+                     (make-user-message
+                      (call-with-input-string
+                          (format #f (W_ "<p>The server hosting your application does not behave correctly, because it lacks the client_id field.<p>"))
+                        xml->sxml)))))
                  (unless (equal? client-id new-client-id)
                    (raise-exception
                     (make-exception
@@ -203,8 +212,10 @@
                       (format #f (G_ "the client manifest under ~s has a client_id of ~s")
                               (uri->string client-id)
                               (uri->string new-client-id)))
-                     (make-message-for-the-user
-                      `(p ,(W_ "The application you want to use does not control the domain name it appears to represent."))))))
+                     (make-user-message
+                      (call-with-input-string
+                          (format #f (W_ "<p>The application you want to use does not control the domain name it appears to represent.</p>"))
+                        xml->sxml)))))
                  (do-initialize new-client-id redirect-uris)))))))
       (else
        (unless (uri? client-id)
@@ -231,16 +242,18 @@
             (format #f (G_ "the client manifest does not allow ~s as a redirection uri")
                     (uri->string redir)))
            (final-user-message
-            (sxml-match
-             (xml->sxml (W_ "<p>The application wants to get your
-authorization through <strong>~s</strong>, which is not
-approved.</p>"))
-             ((*TOP* ,element) element))))
+            (call-with-input-string
+                (format #f (W_ "<p>The application wants to get your
+authorization through <strong>~a</strong>, which is not
+approved.</p>")
+                        (call-with-output-string
+                          (cute sxml->xml `(*TOP* ,(uri->string redir)) <>)))
+              xml->sxml)))
        (raise-exception
         (make-exception
          (make-unauthorized-redirect-uri)
          (make-exception-with-message final-message)
-         (make-message-for-the-user final-user-message)))))
+         (make-user-message final-user-message)))))
     (((? (cute equal? <> redir) redir) _ ...)
      #t)
     ((_ uris ...)
diff --git a/src/scm/webid-oidc/errors.scm b/src/scm/webid-oidc/errors.scm
index aabb6ea..6efc6c8 100644
--- a/src/scm/webid-oidc/errors.scm
+++ b/src/scm/webid-oidc/errors.scm
@@ -25,24 +25,9 @@
   #:declarative? #t
   #:export
   (
-   &message-for-the-user
-   make-message-for-the-user
-   message-for-the-user?
-   user-message
-
    fail
    ))
 
-;; A message to show the user is an XHTML paragraph or equivalent (as
-;; sxml). A div is used to contain multiple messages.
-
-(define-exception-type
-  &message-for-the-user
-  &external-error
-  make-message-for-the-user
-  message-for-the-user?
-  (message user-message))
-
 (define (fail message)
   ;; Like error, but don’t do funny things when message is not a
   ;; string literal
diff --git a/src/scm/webid-oidc/server/endpoint.scm b/src/scm/webid-oidc/server/endpoint.scm
index d327139..9a19ceb 100644
--- a/src/scm/webid-oidc/server/endpoint.scm
+++ b/src/scm/webid-oidc/server/endpoint.scm
@@ -48,8 +48,62 @@
    routed
 
    handle
+
+   &web-exception
+   make-web-exception
+   web-exception?
+   web-exception-code
+   web-exception-reason-phrase
+
+   &caused-by-user
+   make-caused-by-user
+   caused-by-user?
+   caused-by-user-webid
+
+   &user-message
+   make-user-message
+   user-message?
+   user-message-sxml
    ))
 
+(define-exception-type
+  &web-exception
+  &external-error
+  make-web-exception
+  web-exception?
+  (code web-exception-code)
+  (reason-phrase web-exception-reason-phrase))
+
+(define-exception-type
+  &caused-by-user
+  &external-error
+  make-caused-by-user
+  caused-by-user?
+  (webid caused-by-user-webid))
+
+(define-exception-type
+  &user-message
+  &external-error
+  make-user-message
+  user-message?
+  (sxml user-message-one-sxml))
+
+(define (user-message-sxml exn)
+  (let loop ((components (simple-exceptions exn))
+             (gathered '()))
+    (match components
+      (()
+       (match gathered
+         (()
+          `(div ,(W_ "No information available.")))
+         ((= reverse gathered)
+          `(div ,@gathered))))
+      (((? user-message? (= user-message-one-sxml next))
+        components ...)
+       (loop components `(,next ,@gathered)))
+      ((_ components ...)
+       (loop components gathered)))))
+
 (define-class <endpoint> ()
   (host #:init-keyword #:host #:getter host #:init-value #f)
   (path #:init-keyword #:path #:getter path  #:init-value "/"))
@@ -122,12 +176,10 @@
   (let find-router ((routed (routed endpoint)))
     (match routed
       (()
-       (values
-        (build-response
-         #:code 404
-         #:reason-phrase (W_ "Not Found"))
-        #f
-        '()))
+       (raise-exception
+        (make-exception
+         (make-web-exception 404 (W_ "Not Found"))
+         (make-user-message (W_ "The resource could not be found.")))))
       (((and router
              (? (cute relevant? <> request)))
         _ ...)
diff --git a/src/scm/webid-oidc/token-endpoint.scm b/src/scm/webid-oidc/token-endpoint.scm
index a10c843..53ff1cc 100644
--- a/src/scm/webid-oidc/token-endpoint.scm
+++ b/src/scm/webid-oidc/token-endpoint.scm
@@ -16,6 +16,7 @@
 
 (define-module (webid-oidc token-endpoint)
   #:use-module (webid-oidc errors)
+  #:use-module (webid-oidc server endpoint)
   #:use-module (webid-oidc authorization-code)
   #:use-module (webid-oidc dpop-proof)
   #:use-module (webid-oidc jws)
@@ -119,8 +120,8 @@
                               (xml->sxml
                                (W_ (format #f "<p>The refresh token you sent is invalid, or it is already bound to another key.</p>")))
                               ((*TOP* ,p) p))
-                            ,@(if (message-for-the-user? error)
-                                  (user-message error)
+                            ,@(if (user-message? error)
+                                  (list (user-message-sxml error))
                                   '()))))
                    port)))))
             ((invalid-authorization-code? error)
@@ -145,8 +146,8 @@
                               (xml->sxml
                                (W_ (format #f "<p>The authorization code is forged, or expired.</p>")))
                               ((*TOP* ,p) p))
-                            ,@(if (message-for-the-user? error)
-                                  (user-message error)
+                            ,@(if (user-message? error)
+                                  (list (user-message-sxml error))
                                   '()))))
                    port)))))
             ;; Other bad request
@@ -172,8 +173,8 @@
                               (xml->sxml
                                (W_ (format #f "<p>The token request failed.</p>")))
                               ((*TOP* ,p) p))
-                            ,@(if (message-for-the-user? error)
-                                  (user-message error)
+                            ,@(if (user-message? error)
+                                  (list (user-message-sxml error))
                                   '()))))
                    port)))))))
        thunk))))
@@ -231,7 +232,7 @@
                   (make-exception
                    (make-unsupported-grant-type #f)
                    (make-exception-with-message final-message)
-                   (make-message-for-the-user final-user-message)))))
+                   (make-user-message final-user-message)))))
              (receive (webid client-id)
                  (case (string->symbol grant-type)
                    ((authorization_code)
@@ -249,7 +250,7 @@
                                   (make-exception
                                    (make-no-authorization-code)
                                    (make-exception-with-message final-message)
-                                   (make-message-for-the-user final-user-message)))))
+                                   (make-user-message final-user-message)))))
                              (with-exception-handler
                                  (lambda (error)
                                    (raise-exception
@@ -274,7 +275,7 @@
                            (make-exception
                             (make-no-refresh-token)
                             (make-exception-with-message final-message)
-                            (make-message-for-the-user final-user-message)))))
+                            (make-user-message final-user-message)))))
                       (refresh:with-refresh-token
                        refresh-token
                        (jwk dpop)
@@ -293,7 +294,7 @@
                        (make-exception
                         (make-unsupported-grant-type grant-type)
                         (make-exception-with-message final-message)
-                        (make-message-for-the-user final-user-message))))))
+                        (make-user-message final-user-message))))))
                (let ((id-token
                       (issue <id-token>
                              issuer-key