Set up content negociation

To add support for new conversion strategies, edit serve.scm and fetch.scm.

7 files changed, 510 insertions, 343 deletions

diff --git a/doc/webid-oidc.texi b/doc/webid-oidc.texi
index ba23010..a6852a8 100644
--- a/doc/webid-oidc.texi
+++ b/doc/webid-oidc.texi
@@ -49,6 +49,7 @@ Free Documentation License''
 * Decentralized Authentication on the Web::
 * The Json Web Token::
 * Caching on server side::
+* Content negociation::
 * Running an Identity Provider::
 * Running a Resource Server::
 * Running a client::
@@ -369,6 +370,32 @@ The back-end function, @var{http-get}, defaults to that of
 @emph{(web client)}.
 @end deffn
 
+@node Content negociation
+@chapter Content negociation
+There are a number of different available syntaxes for RDF, some being
+simple and human readable like @emph{turtle}, and others more adapted
+to the JavaScript ecosystem like @emph{json-ld}. To help clients both
+from and outside of the JS ecosystem, the server needs to perform
+@dfn{content negociation}, i.e. convert from one content-type to
+another.
+
+@deffn {function from @code{(webid-oidc serve)}} convert @var{client-accepts} @var{server-name} @var{path} @var{content-type} @var{content}
+Convert the resource representation under @var{path} on
+@var{server-name}, which has a given @var{content-type} and
+@var{content}, to a content-type that the @var{client accepts}.
+
+Return 2 values:
+@enumerate
+@item
+the accepted content-type;
+@item
+the content in the given content-type.
+@end enumerate
+
+Currently, the only conversions are from and to @emph{Turtle} and
+@emph{N-Quads}.
+@end deffn
+
 @node Running an Identity Provider
 @chapter Running an Identity Provider
 
@@ -1302,6 +1329,12 @@ If the resource does not exist, @var{real-etag} is set to
 @code{#f}. In this case, an exception of type @code{&path-not-found}
 is also thrown.
 @end deftp
+
+@deftp {exception type} &not-acceptable @var{client-accepts} @var{path} @var{content-type}
+The client wanted a response with a specific set of
+@var{client-accept}ed content-types, but the real @var{content-type}
+of the resource under @var{path} cannot be converted to one of them.
+@end deftp
 @node GNU Free Documentation License
 @appendix GNU Free Documentation License
 
diff --git a/po/fr.po b/po/fr.po
index 2c28f4a..142caf2 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: 2021-07-01 16:40+0200\n"
-"PO-Revision-Date: 2021-07-01 16:40+0200\n"
+"POT-Creation-Date: 2021-07-02 10:57+0200\n"
+"PO-Revision-Date: 2021-07-02 10:59+0200\n"
 "Last-Translator: Vivien Kraus <vivien@planete-kraus.eu>\n"
 "Language-Team: French <vivien@planete-kraus.eu>\n"
 "Language: fr\n"
@@ -126,101 +126,101 @@ msgstr "Utilisation : generate-random [NOMBRE D'OCTETS]\n"
 msgid "Usage: generate-key [NUMBER OF BITS | CURVE]\n"
 msgstr "Utilisation : generate-key [NOMBRE DE BITS | COURBE]\n"
 
-#: src/scm/webid-oidc/errors.scm:1047
+#: src/scm/webid-oidc/errors.scm:1063
 msgid "that’s how it is"
 msgstr "c’est comme ça"
 
-#: src/scm/webid-oidc/errors.scm:1052
+#: src/scm/webid-oidc/errors.scm:1068
 #, scheme-format
 msgid "the value ~s is not a base64 string (because ~a)"
 msgstr "la valeur ~s n’est pas une chaîne base64 (parce que ~a)"
 
-#: src/scm/webid-oidc/errors.scm:1055
+#: src/scm/webid-oidc/errors.scm:1071
 #, scheme-format
 msgid "the value ~s is not JSON (because ~a)"
 msgstr "la valeur ~s n’est pas du JSON (parce que ~a)"
 
-#: src/scm/webid-oidc/errors.scm:1058
+#: src/scm/webid-oidc/errors.scm:1074
 #, scheme-format
 msgid "the value ~s is not Turtle (because ~a)"
 msgstr "la valeur ~s n’est pas du Turtle (parce que ~a)"
 
-#: src/scm/webid-oidc/errors.scm:1061
+#: src/scm/webid-oidc/errors.scm:1077
 #, scheme-format
 msgid "the value ~s does not identify an elleptic curve"
 msgstr "la valeur ~s n’identifie pas une courbe elliptique"
 
-#: src/scm/webid-oidc/errors.scm:1066
+#: src/scm/webid-oidc/errors.scm:1082
 #, scheme-format
 msgid "the value ~s does not identify a JWK (because ~a)"
 msgstr "la valeur ~s n’identifie pas une JWK (parce que ~a)"
 
-#: src/scm/webid-oidc/errors.scm:1068
+#: src/scm/webid-oidc/errors.scm:1084
 #, scheme-format
 msgid "the value ~s does not identify a JWK"
 msgstr "la valeur ~s n’identifie pas une JWK"
 
-#: src/scm/webid-oidc/errors.scm:1073
+#: src/scm/webid-oidc/errors.scm:1089
 #, scheme-format
 msgid "the value ~s does not identify a public JWK (because ~a)"
 msgstr "la valeur ~s n’identifie pas une JWK publique (parce que ~a)"
 
-#: src/scm/webid-oidc/errors.scm:1075
+#: src/scm/webid-oidc/errors.scm:1091
 #, scheme-format
 msgid "the value ~s does not identify a public JWK"
 msgstr "la valeur ~s n’identifie pas une JWK publique"
 
-#: src/scm/webid-oidc/errors.scm:1080
+#: src/scm/webid-oidc/errors.scm:1096
 #, scheme-format
 msgid "the value ~s does not identify a private JWK (because ~a)"
 msgstr "la valeur ~s n’identifie pas une JWK privée (parce que ~a)"
 
-#: src/scm/webid-oidc/errors.scm:1082
+#: src/scm/webid-oidc/errors.scm:1098
 #, scheme-format
 msgid "the value ~s does not identify a private JWK"
 msgstr "la valeur ~s n’identifie pas une JWK privée"
 
-#: src/scm/webid-oidc/errors.scm:1087
+#: src/scm/webid-oidc/errors.scm:1103
 #, scheme-format
 msgid "the value ~s does not identify a JWKS (because ~a)"
 msgstr "la valeur ~s n’identifie pas un JWKS (parce que ~a)"
 
-#: src/scm/webid-oidc/errors.scm:1089
+#: src/scm/webid-oidc/errors.scm:1105
 #, scheme-format
 msgid "the value ~s does not identify a JWKS"
 msgstr "la valeur ~s n’identifie pas un JWKS"
 
-#: src/scm/webid-oidc/errors.scm:1092
+#: src/scm/webid-oidc/errors.scm:1108
 #, scheme-format
 msgid "the value ~s does not identify a hash algorithm"
 msgstr "la valeur ~s n’identifie pas un algorithme de hachage"
 
-#: src/scm/webid-oidc/errors.scm:1095
+#: src/scm/webid-oidc/errors.scm:1111
 #, scheme-format
 msgid "the value ~s is not an alist or misses key ~s"
 msgstr "la valeur ~s n’est pas une alist ou il manque la clé ~s"
 
-#: src/scm/webid-oidc/errors.scm:1098
+#: src/scm/webid-oidc/errors.scm:1114
 #, scheme-format
 msgid "the value ~s is not a JWS header (because ~a)"
 msgstr "la valeur ~s n’est pas un header JWS (parce que ~a)"
 
-#: src/scm/webid-oidc/errors.scm:1101
+#: src/scm/webid-oidc/errors.scm:1117
 #, scheme-format
 msgid "the value ~s is not a JWS payload (because ~a)"
 msgstr "la valeur ~s n’est pas un contenu JWS (parce que ~a)"
 
-#: src/scm/webid-oidc/errors.scm:1104
+#: src/scm/webid-oidc/errors.scm:1120
 #, scheme-format
 msgid "the value ~s is not a JWS (because ~a)"
 msgstr "la valeur ~s n’est pas un JWS (parce que ~a)"
 
-#: src/scm/webid-oidc/errors.scm:1107
+#: src/scm/webid-oidc/errors.scm:1123
 #, scheme-format
 msgid "the string ~s cannot be split in 3 parts with ~s"
 msgstr "la chaîne ~s ne peut pas être découpée en 3 parties avec ~s"
 
-#: src/scm/webid-oidc/errors.scm:1110
+#: src/scm/webid-oidc/errors.scm:1126
 #, scheme-format
 msgid ""
 "all key candidates failed to verify signature ~s with algorithm ~s and "
@@ -229,17 +229,17 @@ msgstr ""
 "aucune clé candidate n’a pu vérifier la signature ~s avec l’algorithme ~s et "
 "le contenu ~a (il y en avait ~a : ~s)"
 
-#: src/scm/webid-oidc/errors.scm:1113
+#: src/scm/webid-oidc/errors.scm:1129
 #, scheme-format
 msgid "I cannot decode JWS ~a (because ~a)"
 msgstr "je n’ai pas pu décoder le JWS encodé par ~a (parce que ~a)"
 
-#: src/scm/webid-oidc/errors.scm:1116
+#: src/scm/webid-oidc/errors.scm:1132
 #, scheme-format
 msgid "I cannot encode JWS ~a (because ~a)"
 msgstr "je n’ai pas pu encoder le JWS ~a (parce que ~a)"
 
-#: src/scm/webid-oidc/errors.scm:1119
+#: src/scm/webid-oidc/errors.scm:1135
 #, scheme-format
 msgid ""
 "the server request unexpectedly failed with code ~a and reason phrase ~s"
@@ -247,338 +247,338 @@ msgstr ""
 "la requête au serveur a échoué de façon inattendue avec un code ~a et une "
 "raison ~s"
 
-#: src/scm/webid-oidc/errors.scm:1124
+#: src/scm/webid-oidc/errors.scm:1140
 #, scheme-format
 msgid "the header ~a should not have the value ~s"
 msgstr "l’en-tête ~a ne devrait pas avoir la valeur ~s"
 
-#: src/scm/webid-oidc/errors.scm:1126
+#: src/scm/webid-oidc/errors.scm:1142
 #, scheme-format
 msgid "the header ~a should be present"
 msgstr "l’en-tête ~a devrait être présent"
 
-#: src/scm/webid-oidc/errors.scm:1129
+#: src/scm/webid-oidc/errors.scm:1145
 #, scheme-format
 msgid "the server response wasn't expected: ~s (because ~a)"
 msgstr "la réponse du serveur est inattendue : ~s (parce que ~a)"
 
-#: src/scm/webid-oidc/errors.scm:1135
+#: src/scm/webid-oidc/errors.scm:1151
 #, scheme-format
 msgid "the value ~s is not an OIDC configuration (because ~a)"
 msgstr "la valeur ~s n’est pas une configuration OIDC (parce que ~a)"
 
-#: src/scm/webid-oidc/errors.scm:1140
+#: src/scm/webid-oidc/errors.scm:1156
 #, scheme-format
 msgid "the webid field is incorrect: ~s"
 msgstr "le champ webid est incorrect : ~s"
 
-#: src/scm/webid-oidc/errors.scm:1141
+#: src/scm/webid-oidc/errors.scm:1157
 msgid "the webid field is missing"
 msgstr "le champ webid est manquant"
 
-#: src/scm/webid-oidc/errors.scm:1145
+#: src/scm/webid-oidc/errors.scm:1161
 #, scheme-format
 msgid "the sub field is incorrect: ~s"
 msgstr "le champ sub est incorrect : ~s"
 
-#: src/scm/webid-oidc/errors.scm:1146
+#: src/scm/webid-oidc/errors.scm:1162
 msgid "the sub field is missing"
 msgstr "le champ sub est manquant"
 
-#: src/scm/webid-oidc/errors.scm:1150
+#: src/scm/webid-oidc/errors.scm:1166
 #, scheme-format
 msgid "the iss field is incorrect: ~s"
 msgstr "le champ iss est incorrect : ~s"
 
-#: src/scm/webid-oidc/errors.scm:1151
+#: src/scm/webid-oidc/errors.scm:1167
 msgid "the iss field is missing"
 msgstr "le champ iss est manquant"
 
-#: src/scm/webid-oidc/errors.scm:1155
+#: src/scm/webid-oidc/errors.scm:1171
 #, scheme-format
 msgid "the aud field is incorrect: ~s"
 msgstr "le champ aud est incorrect : ~s"
 
-#: src/scm/webid-oidc/errors.scm:1156
+#: src/scm/webid-oidc/errors.scm:1172
 msgid "the aud field is missing"
 msgstr "le champ aud est manquant"
 
-#: src/scm/webid-oidc/errors.scm:1160
+#: src/scm/webid-oidc/errors.scm:1176
 #, scheme-format
 msgid "the iat field is incorrect: ~s"
 msgstr "le champ iat est incorrect : ~s"
 
-#: src/scm/webid-oidc/errors.scm:1161
+#: src/scm/webid-oidc/errors.scm:1177
 msgid "the iat field is missing"
 msgstr "le champ iat est manquant"
 
-#: src/scm/webid-oidc/errors.scm:1165
+#: src/scm/webid-oidc/errors.scm:1181
 #, scheme-format
 msgid "the exp field is incorrect: ~s"
 msgstr "le champ exp est incorrect : ~s"
 
-#: src/scm/webid-oidc/errors.scm:1166
+#: src/scm/webid-oidc/errors.scm:1182
 msgid "the exp field is missing"
 msgstr "le champ exp est manquant"
 
-#: src/scm/webid-oidc/errors.scm:1170
+#: src/scm/webid-oidc/errors.scm:1186
 #, scheme-format
 msgid "the cnf/jkt field is incorrect: ~s"
 msgstr "le champ cnf/jkt est incorrect : ~s"
 
-#: src/scm/webid-oidc/errors.scm:1171
+#: src/scm/webid-oidc/errors.scm:1187
 msgid "the cnf/jkt field is missing"
 msgstr "le champ cnf/jkt est manquant"
 
-#: src/scm/webid-oidc/errors.scm:1175
+#: src/scm/webid-oidc/errors.scm:1191
 #, scheme-format
 msgid "the client-id field is incorrect: ~s"
 msgstr "le champ client-id est incorrect : ~s"
 
-#: src/scm/webid-oidc/errors.scm:1176
+#: src/scm/webid-oidc/errors.scm:1192
 msgid "the client-id field is missing"
 msgstr "le champ client-id est manquant"
 
-#: src/scm/webid-oidc/errors.scm:1180
+#: src/scm/webid-oidc/errors.scm:1196
 #: src/scm/webid-oidc/authorization-page-unsafe.scm:149
 #, scheme-format
 msgid "the redirect_uris field is incorrect: ~s"
 msgstr "le champ redirect_uris est incorrect : ~s"
 
-#: src/scm/webid-oidc/errors.scm:1181
+#: src/scm/webid-oidc/errors.scm:1197
 #: src/scm/webid-oidc/authorization-page-unsafe.scm:150
 msgid "the redirect_uris field is missing"
 msgstr "le champ redirect_uris est manquant"
 
-#: src/scm/webid-oidc/errors.scm:1185
+#: src/scm/webid-oidc/errors.scm:1201
 #, scheme-format
 msgid "the typ field is incorrect: ~s"
 msgstr "le champ typ est incorrect : ~s"
 
-#: src/scm/webid-oidc/errors.scm:1186
+#: src/scm/webid-oidc/errors.scm:1202
 msgid "the typ field is missing"
 msgstr "le champ typ est manquant"
 
-#: src/scm/webid-oidc/errors.scm:1190
+#: src/scm/webid-oidc/errors.scm:1206
 #, scheme-format
 msgid "the jwk field is incorrect: ~s (because ~a)"
 msgstr "le champ jwk est incorrect : ~s (parce que ~a)"
 
-#: src/scm/webid-oidc/errors.scm:1192
+#: src/scm/webid-oidc/errors.scm:1208
 msgid "the jwk field is missing"
 msgstr "le champ jwk est manquant"
 
-#: src/scm/webid-oidc/errors.scm:1196
+#: src/scm/webid-oidc/errors.scm:1212
 #, scheme-format
 msgid "the jti field is incorrect: ~s"
 msgstr "le champ jti est incorrect : ~s"
 
-#: src/scm/webid-oidc/errors.scm:1197
+#: src/scm/webid-oidc/errors.scm:1213
 msgid "the jti field is missing"
 msgstr "le champ jti est manquant"
 
-#: src/scm/webid-oidc/errors.scm:1201
+#: src/scm/webid-oidc/errors.scm:1217
 #, scheme-format
 msgid "the nonce field is incorrect: ~s"
 msgstr "le champ nonce est incorrect : ~s"
 
-#: src/scm/webid-oidc/errors.scm:1202
+#: src/scm/webid-oidc/errors.scm:1218
 msgid "the nonce field is missing"
 msgstr "le champ nonce est manquant"
 
-#: src/scm/webid-oidc/errors.scm:1206
+#: src/scm/webid-oidc/errors.scm:1222
 #, scheme-format
 msgid "the htm field is incorrect: ~s"
 msgstr "le champ htm est incorrect : ~s"
 
-#: src/scm/webid-oidc/errors.scm:1207
+#: src/scm/webid-oidc/errors.scm:1223
 msgid "the htm field is missing"
 msgstr "le champ htm est manquant"
 
-#: src/scm/webid-oidc/errors.scm:1211
+#: src/scm/webid-oidc/errors.scm:1227
 #, scheme-format
 msgid "the htu field is incorrect: ~s"
 msgstr "le champ htu est incorrect : ~s"
 
-#: src/scm/webid-oidc/errors.scm:1212
+#: src/scm/webid-oidc/errors.scm:1228
 msgid "the htu field is missing"
 msgstr "le champ htu est manquant"
 
-#: src/scm/webid-oidc/errors.scm:1214
+#: src/scm/webid-oidc/errors.scm:1230
 #, scheme-format
 msgid "~s is not an access token (because ~a)"
 msgstr "~s n’est pas un jeton d’accès (parce que ~a)"
 
-#: src/scm/webid-oidc/errors.scm:1217
+#: src/scm/webid-oidc/errors.scm:1233
 #, scheme-format
 msgid "~s is not an access token header (because ~a)"
 msgstr "~s n’est pas un en-tête de jeton d’accès (parce que ~a)"
 
-#: src/scm/webid-oidc/errors.scm:1220
+#: src/scm/webid-oidc/errors.scm:1236
 #, scheme-format
 msgid "~s is not an access token payload (because ~a)"
 msgstr "~s n’est pas un contenu de jeton d’accès (parce que ~a)"
 
-#: src/scm/webid-oidc/errors.scm:1223
+#: src/scm/webid-oidc/errors.scm:1239
 #, scheme-format
 msgid "~s is not a DPoP proof (because ~a)"
 msgstr "~s n’est pas une preuve DPoP (parce que ~a)"
 
-#: src/scm/webid-oidc/errors.scm:1226
+#: src/scm/webid-oidc/errors.scm:1242
 #, scheme-format
 msgid "~s is not a DPoP proof header (because ~a)"
 msgstr "~s n’est pas un en-tête de preuve DPoP (parce que ~a)"
 
-#: src/scm/webid-oidc/errors.scm:1229
+#: src/scm/webid-oidc/errors.scm:1245
 #, scheme-format
 msgid "~s is not a DPoP proof payload (because ~a)"
 msgstr "~s n’est pas un contenu de preuve DPoP (parce que ~a)"
 
-#: src/scm/webid-oidc/errors.scm:1232
+#: src/scm/webid-oidc/errors.scm:1248
 #, scheme-format
 msgid "I cannot fetch the issuer configuration of ~a (because ~a)"
 msgstr ""
 "je n’ai pas pu récupérer la configuration de l’émetteur ~a (parce que ~a)"
 
-#: src/scm/webid-oidc/errors.scm:1239
+#: src/scm/webid-oidc/errors.scm:1255
 #, scheme-format
 msgid "I cannot fetch the JWKS of ~a at ~a (because ~a)"
 msgstr "je n’ai pas pu récupérer le JWKS de ~a à ~a (parce que ~a)"
 
-#: src/scm/webid-oidc/errors.scm:1250
+#: src/scm/webid-oidc/errors.scm:1266
 #, scheme-format
 msgid "the HTTP method is signed for ~s, but ~s was requested"
 msgstr "la méthode HTTP a été signée pour ~s, mais ~s a été demandé"
 
-#: src/scm/webid-oidc/errors.scm:1253
+#: src/scm/webid-oidc/errors.scm:1269
 #, scheme-format
 msgid "the HTTP uri is signed for ~a, but ~a was requested"
 msgstr "l’uri HTTP a été signé pour ~a, mais ~a a été demandé"
 
-#: src/scm/webid-oidc/errors.scm:1256
+#: src/scm/webid-oidc/errors.scm:1272
 #, scheme-format
 msgid "the date is ~a, but the DPoP proof is signed in the future at ~a"
 msgstr "la date est ~a, mais la preuve DPoP a été signée dans le futur à ~a"
 
-#: src/scm/webid-oidc/errors.scm:1260
+#: src/scm/webid-oidc/errors.scm:1276
 #, scheme-format
 msgid "the date is ~a, but the DPoP proof was signed too long ago at ~a"
 msgstr ""
 "la date est ~a, mais la preuve DPoP a été signée il y a trop longtemps à ~a"
 
-#: src/scm/webid-oidc/errors.scm:1269
+#: src/scm/webid-oidc/errors.scm:1285
 #, scheme-format
 msgid "the key ~s does not hash to ~a"
 msgstr "la clé ~s ne donne pas un hash de ~a"
 
-#: src/scm/webid-oidc/errors.scm:1271
+#: src/scm/webid-oidc/errors.scm:1287
 #, scheme-format
 msgid "the key confirmation of ~s failed (because ~a)"
 msgstr "la confirmation de clé de ~s a échoué (parce que ~a)"
 
-#: src/scm/webid-oidc/errors.scm:1273
+#: src/scm/webid-oidc/errors.scm:1289
 #, scheme-format
 msgid "the key confirmation of ~s failed"
 msgstr "la confirmation de la clé ~s a échoué"
 
-#: src/scm/webid-oidc/errors.scm:1275
+#: src/scm/webid-oidc/errors.scm:1291
 #, scheme-format
 msgid "the jti ~s has already been found (because ~a)"
 msgstr "le jti ~s a déjà été trouvé (parce que ~a)"
 
-#: src/scm/webid-oidc/errors.scm:1278
+#: src/scm/webid-oidc/errors.scm:1294
 #, scheme-format
 msgid "I cannot decode ~s as an access token (because ~a)"
 msgstr "je n’ai pas pu décoder ~s comme jeton d’accès (parce que ~a)"
 
-#: src/scm/webid-oidc/errors.scm:1281
+#: src/scm/webid-oidc/errors.scm:1297
 #, scheme-format
 msgid "I cannot encode ~s as an access token with key ~s (because ~a)"
 msgstr ""
 "je n’ai pas pu encoder ~s comme un jeton d’accès avec la clé ~s (parce que "
 "~a)"
 
-#: src/scm/webid-oidc/errors.scm:1284
+#: src/scm/webid-oidc/errors.scm:1300
 #, scheme-format
 msgid "I cannot decode ~s as a DPoP proof (because ~a)"
 msgstr "je n’ai pas pu décoder ~s comme preuve DPoP (parce que ~a)"
 
-#: src/scm/webid-oidc/errors.scm:1287
+#: src/scm/webid-oidc/errors.scm:1303
 #, scheme-format
 msgid "I cannot encode ~s as a DPoP proof (because ~a)"
 msgstr "je n’ai pas pu encoder ~s comme une preuve DPoP (parce que ~a)"
 
-#: src/scm/webid-oidc/errors.scm:1290
+#: src/scm/webid-oidc/errors.scm:1306
 #, scheme-format
 msgid "I could not fetch a RDF graph at ~a (because ~a)"
 msgstr "je n’ai pas pu récupérer de graphe RDF à ~a (parce que ~a)"
 
-#: src/scm/webid-oidc/errors.scm:1293
+#: src/scm/webid-oidc/errors.scm:1309
 #, scheme-format
 msgid "~s is not a client manifest (because ~a)"
 msgstr "~s n’est pas un manifeste client (parce que ~a)"
 
-#: src/scm/webid-oidc/errors.scm:1296
+#: src/scm/webid-oidc/errors.scm:1312
 #, scheme-format
 msgid "~s does not authorize redirection URI ~a"
 msgstr "~s n’autorise pas l’URI de redirection ~a"
 
-#: src/scm/webid-oidc/errors.scm:1299
+#: src/scm/webid-oidc/errors.scm:1315
 msgid "I cannot serve a public manifest"
 msgstr "je ne peux pas servir un manifeste public"
 
-#: src/scm/webid-oidc/errors.scm:1301
+#: src/scm/webid-oidc/errors.scm:1317
 #, scheme-format
 msgid "~a does not have a client manifest registration triple"
 msgstr "~a n’a pas de triplet d’enregistrement de manifeste client"
 
-#: src/scm/webid-oidc/errors.scm:1304
+#: src/scm/webid-oidc/errors.scm:1320
 #, scheme-format
 msgid "the client manifest at ~a is advertised for ~a"
 msgstr "le manifeste client ~a est publié pour ~a"
 
-#: src/scm/webid-oidc/errors.scm:1307
+#: src/scm/webid-oidc/errors.scm:1323
 #, scheme-format
 msgid "I could not fetch the client manifest of ~a (because ~a)"
 msgstr "je n’ai pas pu récupérer le manifeste client de ~a (parce que ~a)"
 
-#: src/scm/webid-oidc/errors.scm:1310
+#: src/scm/webid-oidc/errors.scm:1326
 #, scheme-format
 msgid "~s is not an authorization code (because ~a)"
 msgstr "~s n’est pas un code d’autorisation (parce que ~a)"
 
-#: src/scm/webid-oidc/errors.scm:1313
+#: src/scm/webid-oidc/errors.scm:1329
 #, scheme-format
 msgid "~s is not an authorization code header (because ~a)"
 msgstr "~s n’est pas un en-tête de code d’autorisation (parce que ~a)"
 
-#: src/scm/webid-oidc/errors.scm:1316
+#: src/scm/webid-oidc/errors.scm:1332
 #, scheme-format
 msgid "~s is not an authorization code payload (because ~a)"
 msgstr "~s n’est pas un contenu de code d’autorisation (parce que ~a)"
 
-#: src/scm/webid-oidc/errors.scm:1319
+#: src/scm/webid-oidc/errors.scm:1335
 #, scheme-format
 msgid "the current time is ~a, and the authorization code expired at ~a"
 msgstr ""
 "la date est actuellement ~a, et le code d’autorisation a expiré à la date ~a"
 
-#: src/scm/webid-oidc/errors.scm:1323
+#: src/scm/webid-oidc/errors.scm:1339
 #, scheme-format
 msgid "I cannot decode ~s as an authorization code (because ~a)"
 msgstr "je n’ai pas pu décoder ~s comme un code d’autorisation (parce que ~a)"
 
-#: src/scm/webid-oidc/errors.scm:1326
+#: src/scm/webid-oidc/errors.scm:1342
 #, scheme-format
 msgid "I cannot encode ~s as an authorization code (because ~a)"
 msgstr "je n’ai pas pu encoder ~s comme un code d’autorisation (parce que ~a)"
 
-#: src/scm/webid-oidc/errors.scm:1329
+#: src/scm/webid-oidc/errors.scm:1345
 #, scheme-format
 msgid "there is no such refresh token as ~s"
 msgstr "il n’y a pas de jeton de rafraîchissement ~s"
 
-#: src/scm/webid-oidc/errors.scm:1332
+#: src/scm/webid-oidc/errors.scm:1348
 #, scheme-format
 msgid ""
 "the refresh token is bound to a key confirmed as ~s, but it is used with key "
@@ -587,45 +587,45 @@ msgstr ""
 "Le jeton de rafraîchissement est lié à une clé confirmée par ~s, mais il est "
 "utilisé avec la clé ~s"
 
-#: src/scm/webid-oidc/errors.scm:1335
+#: src/scm/webid-oidc/errors.scm:1351
 #, scheme-format
 msgid "I cannot decode ~s as an ID token (because ~a)"
 msgstr "je n’ai pas pu décoder ~s comme jeton d’identité (parce que ~a)"
 
-#: src/scm/webid-oidc/errors.scm:1338
+#: src/scm/webid-oidc/errors.scm:1354
 #, scheme-format
 msgid "I cannot encode ~s as an ID token (because ~a)"
 msgstr "je n’ai pas pu encoder ~s comme un jeton d’identité (parce que ~a)"
 
-#: src/scm/webid-oidc/errors.scm:1341
+#: src/scm/webid-oidc/errors.scm:1357
 #, scheme-format
 msgid "the grant type ~s is not supported"
 msgstr "le type d’octroi ~s n’est pas supporté "
 
-#: src/scm/webid-oidc/errors.scm:1344
+#: src/scm/webid-oidc/errors.scm:1360
 msgid "there is no authorization code in the request"
 msgstr "il n’y a pas de code d’autorisation dans la requête"
 
-#: src/scm/webid-oidc/errors.scm:1346
+#: src/scm/webid-oidc/errors.scm:1362
 msgid "there is no refresh token in the request"
 msgstr "il n’y a pas de jeton de rafraîchissement dans la requête"
 
-#: src/scm/webid-oidc/errors.scm:1348
+#: src/scm/webid-oidc/errors.scm:1364
 #, scheme-format
 msgid "~s is not an ID token (because ~a)"
 msgstr "~s n’est pas un jeton d’identité (parce que ~a)"
 
-#: src/scm/webid-oidc/errors.scm:1351
+#: src/scm/webid-oidc/errors.scm:1367
 #, scheme-format
 msgid "~s is not an ID token header (because ~a)"
 msgstr "~s n’est pas un en-tête de jeton d’identité (parce que ~a)"
 
-#: src/scm/webid-oidc/errors.scm:1354
+#: src/scm/webid-oidc/errors.scm:1370
 #, scheme-format
 msgid "~s is not an ID token payload (because ~a)"
 msgstr "~s n’est pas un contenu de jeton d’identité (parce que ~a)"
 
-#: src/scm/webid-oidc/errors.scm:1357
+#: src/scm/webid-oidc/errors.scm:1373
 #, scheme-format
 msgid ""
 "I couldn’t set the locale to ~s as an approximation of the client locale ~s"
@@ -633,12 +633,12 @@ msgstr ""
 "je n’ai pas pu définir la locale à ~s comme approximation de la locale du "
 "client ~s"
 
-#: src/scm/webid-oidc/errors.scm:1360
+#: src/scm/webid-oidc/errors.scm:1376
 #, scheme-format
 msgid "~s does not admit ~s as an identity provider"
 msgstr "~s n’admet pas ~s comme fournisseur d’identité"
 
-#: src/scm/webid-oidc/errors.scm:1363
+#: src/scm/webid-oidc/errors.scm:1379
 #, scheme-format
 msgid ""
 "~a is neither an identity provider (because ~a) nor a webid (because ~a)"
@@ -646,76 +646,76 @@ msgstr ""
 "~a n’est ni un fournisseur d’identité (parce que ~a) ni un webid (parce que "
 "~a)"
 
-#: src/scm/webid-oidc/errors.scm:1368
+#: src/scm/webid-oidc/errors.scm:1384
 #, scheme-format
 msgid "the token request failed (because ~a)"
 msgstr "la requête de jeton a échoué (parce que ~a)"
 
-#: src/scm/webid-oidc/errors.scm:1371
+#: src/scm/webid-oidc/errors.scm:1387
 #, scheme-format
 msgid "you don’t have a refresh token for identity ~a certified by ~a in ~s"
 msgstr ""
 "vous n’avez pas de jeton de rafraîchissement pour l’identité ~a certifié par "
 "~a dans ~s"
 
-#: src/scm/webid-oidc/errors.scm:1376
+#: src/scm/webid-oidc/errors.scm:1392
 #, scheme-format
 msgid "all identity provider candidates for ~a failed: ~a"
 msgstr "tous les candidats de fournisseurs d’identité pour ~a ont échoué : ~a"
 
-#: src/scm/webid-oidc/errors.scm:1380
+#: src/scm/webid-oidc/errors.scm:1396
 #, scheme-format
 msgid "~s failed (because ~a)"
 msgstr "~s a échoué (parce que ~a)"
 
-#: src/scm/webid-oidc/errors.scm:1383
+#: src/scm/webid-oidc/errors.scm:1399
 msgid ", "
 msgstr ", "
 
-#: src/scm/webid-oidc/errors.scm:1385
+#: src/scm/webid-oidc/errors.scm:1401
 #, scheme-format
 msgid "no resource has been found to serve URI path ~s"
 msgstr "aucune ressource n’a été trouvée pour servir le chemin d’URI ~s"
 
-#: src/scm/webid-oidc/errors.scm:1388
+#: src/scm/webid-oidc/errors.scm:1404
 #, scheme-format
 msgid "the resource kind ~s is absent for the resource at ~s"
 msgstr "le type de ressource ~s est absent pour la ressource ~s"
 
-#: src/scm/webid-oidc/errors.scm:1391
+#: src/scm/webid-oidc/errors.scm:1407
 #, scheme-format
 msgid "no resource has been found to serve URI path ~s, but ~s exists"
 msgstr ""
 "aucune ressource n’a été trouvée pour servir le chemin d’URI ~s, mais ~s "
 "existe"
 
-#: src/scm/webid-oidc/errors.scm:1394
+#: src/scm/webid-oidc/errors.scm:1410
 msgid "the root storage cannot be deleted"
 msgstr "le stockage racine ne peut pas être détruit"
 
-#: src/scm/webid-oidc/errors.scm:1396
+#: src/scm/webid-oidc/errors.scm:1412
 #, scheme-format
 msgid "the container ~s should be emptied before being deleted"
 msgstr "le conteneur ~s doit être vidé avant d’être détruit"
 
-#: src/scm/webid-oidc/errors.scm:1399
+#: src/scm/webid-oidc/errors.scm:1415
 #, scheme-format
 msgid "the group ~s cannot be fetched (because ~a)"
 msgstr "le groupe ~s n’a pas pu être récupéré (parce que ~a)"
 
-#: src/scm/webid-oidc/errors.scm:1403
+#: src/scm/webid-oidc/errors.scm:1419
 #, scheme-format
 msgid "the containment triples in the request to update ~s are not up to date"
 msgstr ""
 "les triplets de contention dans la requête pour changer ~s ne sont pas à jour"
 
-#: src/scm/webid-oidc/errors.scm:1406
+#: src/scm/webid-oidc/errors.scm:1422
 #, scheme-format
 msgid "the server cannot process resources with the ~s content-type"
 msgstr ""
 "le serveur ne peut pas traiter des ressources avec le type de contenu ~s"
 
-#: src/scm/webid-oidc/errors.scm:1409
+#: src/scm/webid-oidc/errors.scm:1425
 #, scheme-format
 msgid ""
 "the client wants to create a resource at ~s, which is reserved for an "
@@ -724,7 +724,7 @@ msgstr ""
 "le client veut créer une ressource en tant que ~s, qui est réservé pour une "
 "ressource auxiliare"
 
-#: src/scm/webid-oidc/errors.scm:1412
+#: src/scm/webid-oidc/errors.scm:1428
 #, scheme-format
 msgid ""
 "the operation on ~s by ~a is refused, because it’s not by ~s and the access "
@@ -733,11 +733,11 @@ msgstr ""
 "l’opération sur ~s par ~a est refusée, parce que ce n’est pas ~s et le "
 "contrôle d’accès refuse le mode d’opération suivant : ~s"
 
-#: src/scm/webid-oidc/errors.scm:1416
+#: src/scm/webid-oidc/errors.scm:1432
 msgid "an anonymous user"
 msgstr "un utilisateur anonyme"
 
-#: src/scm/webid-oidc/errors.scm:1421
+#: src/scm/webid-oidc/errors.scm:1437
 #, scheme-format
 msgid ""
 "the client precondition failed for ~s: it allows for ~s, forbids ~s, but the "
@@ -746,7 +746,7 @@ msgstr ""
 "la précondition du client a échoué pour ~s : elle autorise ~s, interdit ~s, "
 "mais la ressource a une représentation ~s"
 
-#: src/scm/webid-oidc/errors.scm:1423
+#: src/scm/webid-oidc/errors.scm:1439
 #, scheme-format
 msgid ""
 "the client precondition failed for ~s: it allows for ~s, forbids ~s, but the "
@@ -755,71 +755,81 @@ msgstr ""
 "la précondition du client a échoué pour ~s : elle autorise ~s, interdit ~s, "
 "mais la ressource n’a pas de représentation"
 
-#: src/scm/webid-oidc/errors.scm:1428
+#: src/scm/webid-oidc/errors.scm:1442
+#, scheme-format
+msgid ""
+"the client wanted a response with a content type among ~s, but the resource "
+"at ~s has content-type ~s which cannot be converted to one of them"
+msgstr ""
+"le client voulait une réponse avec un type de contenu parmi ~s, mais la "
+"ressource ~s a un type de contenu ~s qui ne peut pas être converti vers l’un "
+"d’eux"
+
+#: src/scm/webid-oidc/errors.scm:1449
 msgid "that’s it"
 msgstr "c’est tout"
 
-#: src/scm/webid-oidc/errors.scm:1432
+#: src/scm/webid-oidc/errors.scm:1453
 #, scheme-format
 msgid "~a and ~a"
 msgstr "~a et ~a"
 
-#: src/scm/webid-oidc/errors.scm:1435
+#: src/scm/webid-oidc/errors.scm:1456
 #, scheme-format
 msgid "~a, ~a"
 msgstr "~a, ~a"
 
-#: src/scm/webid-oidc/errors.scm:1439
+#: src/scm/webid-oidc/errors.scm:1460
 #, scheme-format
 msgid "the signature ~a does not match key ~s with payload ~a"
 msgstr "la signature ~a ne correspond pas à la clé ~s avec le contenu ~a"
 
-#: src/scm/webid-oidc/errors.scm:1442
+#: src/scm/webid-oidc/errors.scm:1463
 msgid "there is an undefined variable"
 msgstr "il y a une variable non définie"
 
-#: src/scm/webid-oidc/errors.scm:1444
+#: src/scm/webid-oidc/errors.scm:1465
 #, scheme-format
 msgid "the origin is ~a"
 msgstr "l’origine est ~a"
 
-#: src/scm/webid-oidc/errors.scm:1447
+#: src/scm/webid-oidc/errors.scm:1468
 #, scheme-format
 msgid "a message is attached: ~a"
 msgstr "un message est attaché : ~a"
 
-#: src/scm/webid-oidc/errors.scm:1450
+#: src/scm/webid-oidc/errors.scm:1471
 #, scheme-format
 msgid "the values ~s are problematic"
 msgstr "les valeurs ~s sont problématiques"
 
-#: src/scm/webid-oidc/errors.scm:1453
+#: src/scm/webid-oidc/errors.scm:1474
 #, scheme-format
 msgid "there is a kind (~s) and args ~s"
 msgstr "il y a un type (~s) et des arguments ~s"
 
-#: src/scm/webid-oidc/errors.scm:1456
+#: src/scm/webid-oidc/errors.scm:1477
 msgid "there is an assertion failure"
 msgstr "il y a un échec d’assertion"
 
-#: src/scm/webid-oidc/errors.scm:1458
+#: src/scm/webid-oidc/errors.scm:1479
 #, scheme-format
 msgid "the program quits with code ~a"
 msgstr "le programme quitte avec le code ~a"
 
-#: src/scm/webid-oidc/errors.scm:1461
+#: src/scm/webid-oidc/errors.scm:1482
 msgid "the program cannot recover from this exception"
 msgstr "le programme ne peut pas récupérer après cette exception"
 
-#: src/scm/webid-oidc/errors.scm:1463
+#: src/scm/webid-oidc/errors.scm:1484
 msgid "there is an external error"
 msgstr "il y a une erreur externe"
 
-#: src/scm/webid-oidc/errors.scm:1465
+#: src/scm/webid-oidc/errors.scm:1486
 msgid "there is an error"
 msgstr "il y a une erreur"
 
-#: src/scm/webid-oidc/errors.scm:1467
+#: src/scm/webid-oidc/errors.scm:1488
 #, scheme-format
 msgid "Unhandled exception type ~a."
 msgstr "Type d’exception non pris en charge ~a."
@@ -966,17 +976,17 @@ msgstr ""
 "<a href=~s>~a</a> peut maintenant s'identifier en votre nom. Vous devez "
 "toujours ajuster ses permissions."
 
-#: src/scm/webid-oidc/resource-server.scm:91
+#: src/scm/webid-oidc/resource-server.scm:92
 #, scheme-format
 msgid "~a: authentication failure: ~a\n"
 msgstr "~a : échec d’authentificationn : ~a\n"
 
-#: src/scm/webid-oidc/resource-server.scm:220
+#: src/scm/webid-oidc/resource-server.scm:237
 #, scheme-format
 msgid "Warning: ~a\n"
 msgstr "Avertissement : ~a\n"
 
-#: src/scm/webid-oidc/resource-server.scm:223
+#: src/scm/webid-oidc/resource-server.scm:240
 #, scheme-format
 msgid "Error: ~a\n"
 msgstr "Erreur : ~a\n"
diff --git a/po/webid-oidc.pot b/po/webid-oidc.pot
index 89b625c..985c688 100644
--- a/po/webid-oidc.pot
+++ b/po/webid-oidc.pot
@@ -8,7 +8,7 @@ msgid ""
 msgstr ""
 "Project-Id-Version: webid-oidc SNAPSHOT\n"
 "Report-Msgid-Bugs-To: vivien@planete-kraus.eu\n"
-"POT-Creation-Date: 2021-07-01 16:40+0200\n"
+"POT-Creation-Date: 2021-07-02 10:57+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"
@@ -122,671 +122,678 @@ msgstr ""
 msgid "Usage: generate-key [NUMBER OF BITS | CURVE]\n"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1047
+#: src/scm/webid-oidc/errors.scm:1063
 msgid "that’s how it is"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1052
+#: src/scm/webid-oidc/errors.scm:1068
 #, scheme-format
 msgid "the value ~s is not a base64 string (because ~a)"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1055
+#: src/scm/webid-oidc/errors.scm:1071
 #, scheme-format
 msgid "the value ~s is not JSON (because ~a)"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1058
+#: src/scm/webid-oidc/errors.scm:1074
 #, scheme-format
 msgid "the value ~s is not Turtle (because ~a)"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1061
+#: src/scm/webid-oidc/errors.scm:1077
 #, scheme-format
 msgid "the value ~s does not identify an elleptic curve"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1066
+#: src/scm/webid-oidc/errors.scm:1082
 #, scheme-format
 msgid "the value ~s does not identify a JWK (because ~a)"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1068
+#: src/scm/webid-oidc/errors.scm:1084
 #, scheme-format
 msgid "the value ~s does not identify a JWK"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1073
+#: src/scm/webid-oidc/errors.scm:1089
 #, scheme-format
 msgid "the value ~s does not identify a public JWK (because ~a)"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1075
+#: src/scm/webid-oidc/errors.scm:1091
 #, scheme-format
 msgid "the value ~s does not identify a public JWK"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1080
+#: src/scm/webid-oidc/errors.scm:1096
 #, scheme-format
 msgid "the value ~s does not identify a private JWK (because ~a)"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1082
+#: src/scm/webid-oidc/errors.scm:1098
 #, scheme-format
 msgid "the value ~s does not identify a private JWK"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1087
+#: src/scm/webid-oidc/errors.scm:1103
 #, scheme-format
 msgid "the value ~s does not identify a JWKS (because ~a)"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1089
+#: src/scm/webid-oidc/errors.scm:1105
 #, scheme-format
 msgid "the value ~s does not identify a JWKS"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1092
+#: src/scm/webid-oidc/errors.scm:1108
 #, scheme-format
 msgid "the value ~s does not identify a hash algorithm"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1095
+#: src/scm/webid-oidc/errors.scm:1111
 #, scheme-format
 msgid "the value ~s is not an alist or misses key ~s"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1098
+#: src/scm/webid-oidc/errors.scm:1114
 #, scheme-format
 msgid "the value ~s is not a JWS header (because ~a)"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1101
+#: src/scm/webid-oidc/errors.scm:1117
 #, scheme-format
 msgid "the value ~s is not a JWS payload (because ~a)"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1104
+#: src/scm/webid-oidc/errors.scm:1120
 #, scheme-format
 msgid "the value ~s is not a JWS (because ~a)"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1107
+#: src/scm/webid-oidc/errors.scm:1123
 #, scheme-format
 msgid "the string ~s cannot be split in 3 parts with ~s"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1110
+#: src/scm/webid-oidc/errors.scm:1126
 #, scheme-format
 msgid ""
 "all key candidates failed to verify signature ~s with algorithm ~s and "
 "payload ~a (there were ~a: ~s)"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1113
+#: src/scm/webid-oidc/errors.scm:1129
 #, scheme-format
 msgid "I cannot decode JWS ~a (because ~a)"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1116
+#: src/scm/webid-oidc/errors.scm:1132
 #, scheme-format
 msgid "I cannot encode JWS ~a (because ~a)"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1119
+#: src/scm/webid-oidc/errors.scm:1135
 #, scheme-format
 msgid ""
 "the server request unexpectedly failed with code ~a and reason phrase ~s"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1124
+#: src/scm/webid-oidc/errors.scm:1140
 #, scheme-format
 msgid "the header ~a should not have the value ~s"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1126
+#: src/scm/webid-oidc/errors.scm:1142
 #, scheme-format
 msgid "the header ~a should be present"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1129
+#: src/scm/webid-oidc/errors.scm:1145
 #, scheme-format
 msgid "the server response wasn't expected: ~s (because ~a)"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1135
+#: src/scm/webid-oidc/errors.scm:1151
 #, scheme-format
 msgid "the value ~s is not an OIDC configuration (because ~a)"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1140
+#: src/scm/webid-oidc/errors.scm:1156
 #, scheme-format
 msgid "the webid field is incorrect: ~s"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1141
+#: src/scm/webid-oidc/errors.scm:1157
 msgid "the webid field is missing"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1145
+#: src/scm/webid-oidc/errors.scm:1161
 #, scheme-format
 msgid "the sub field is incorrect: ~s"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1146
+#: src/scm/webid-oidc/errors.scm:1162
 msgid "the sub field is missing"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1150
+#: src/scm/webid-oidc/errors.scm:1166
 #, scheme-format
 msgid "the iss field is incorrect: ~s"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1151
+#: src/scm/webid-oidc/errors.scm:1167
 msgid "the iss field is missing"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1155
+#: src/scm/webid-oidc/errors.scm:1171
 #, scheme-format
 msgid "the aud field is incorrect: ~s"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1156
+#: src/scm/webid-oidc/errors.scm:1172
 msgid "the aud field is missing"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1160
+#: src/scm/webid-oidc/errors.scm:1176
 #, scheme-format
 msgid "the iat field is incorrect: ~s"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1161
+#: src/scm/webid-oidc/errors.scm:1177
 msgid "the iat field is missing"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1165
+#: src/scm/webid-oidc/errors.scm:1181
 #, scheme-format
 msgid "the exp field is incorrect: ~s"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1166
+#: src/scm/webid-oidc/errors.scm:1182
 msgid "the exp field is missing"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1170
+#: src/scm/webid-oidc/errors.scm:1186
 #, scheme-format
 msgid "the cnf/jkt field is incorrect: ~s"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1171
+#: src/scm/webid-oidc/errors.scm:1187
 msgid "the cnf/jkt field is missing"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1175
+#: src/scm/webid-oidc/errors.scm:1191
 #, scheme-format
 msgid "the client-id field is incorrect: ~s"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1176
+#: src/scm/webid-oidc/errors.scm:1192
 msgid "the client-id field is missing"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1180
+#: src/scm/webid-oidc/errors.scm:1196
 #: src/scm/webid-oidc/authorization-page-unsafe.scm:149
 #, scheme-format
 msgid "the redirect_uris field is incorrect: ~s"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1181
+#: src/scm/webid-oidc/errors.scm:1197
 #: src/scm/webid-oidc/authorization-page-unsafe.scm:150
 msgid "the redirect_uris field is missing"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1185
+#: src/scm/webid-oidc/errors.scm:1201
 #, scheme-format
 msgid "the typ field is incorrect: ~s"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1186
+#: src/scm/webid-oidc/errors.scm:1202
 msgid "the typ field is missing"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1190
+#: src/scm/webid-oidc/errors.scm:1206
 #, scheme-format
 msgid "the jwk field is incorrect: ~s (because ~a)"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1192
+#: src/scm/webid-oidc/errors.scm:1208
 msgid "the jwk field is missing"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1196
+#: src/scm/webid-oidc/errors.scm:1212
 #, scheme-format
 msgid "the jti field is incorrect: ~s"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1197
+#: src/scm/webid-oidc/errors.scm:1213
 msgid "the jti field is missing"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1201
+#: src/scm/webid-oidc/errors.scm:1217
 #, scheme-format
 msgid "the nonce field is incorrect: ~s"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1202
+#: src/scm/webid-oidc/errors.scm:1218
 msgid "the nonce field is missing"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1206
+#: src/scm/webid-oidc/errors.scm:1222
 #, scheme-format
 msgid "the htm field is incorrect: ~s"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1207
+#: src/scm/webid-oidc/errors.scm:1223
 msgid "the htm field is missing"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1211
+#: src/scm/webid-oidc/errors.scm:1227
 #, scheme-format
 msgid "the htu field is incorrect: ~s"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1212
+#: src/scm/webid-oidc/errors.scm:1228
 msgid "the htu field is missing"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1214
+#: src/scm/webid-oidc/errors.scm:1230
 #, scheme-format
 msgid "~s is not an access token (because ~a)"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1217
+#: src/scm/webid-oidc/errors.scm:1233
 #, scheme-format
 msgid "~s is not an access token header (because ~a)"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1220
+#: src/scm/webid-oidc/errors.scm:1236
 #, scheme-format
 msgid "~s is not an access token payload (because ~a)"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1223
+#: src/scm/webid-oidc/errors.scm:1239
 #, scheme-format
 msgid "~s is not a DPoP proof (because ~a)"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1226
+#: src/scm/webid-oidc/errors.scm:1242
 #, scheme-format
 msgid "~s is not a DPoP proof header (because ~a)"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1229
+#: src/scm/webid-oidc/errors.scm:1245
 #, scheme-format
 msgid "~s is not a DPoP proof payload (because ~a)"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1232
+#: src/scm/webid-oidc/errors.scm:1248
 #, scheme-format
 msgid "I cannot fetch the issuer configuration of ~a (because ~a)"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1239
+#: src/scm/webid-oidc/errors.scm:1255
 #, scheme-format
 msgid "I cannot fetch the JWKS of ~a at ~a (because ~a)"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1250
+#: src/scm/webid-oidc/errors.scm:1266
 #, scheme-format
 msgid "the HTTP method is signed for ~s, but ~s was requested"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1253
+#: src/scm/webid-oidc/errors.scm:1269
 #, scheme-format
 msgid "the HTTP uri is signed for ~a, but ~a was requested"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1256
+#: src/scm/webid-oidc/errors.scm:1272
 #, scheme-format
 msgid "the date is ~a, but the DPoP proof is signed in the future at ~a"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1260
+#: src/scm/webid-oidc/errors.scm:1276
 #, scheme-format
 msgid "the date is ~a, but the DPoP proof was signed too long ago at ~a"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1269
+#: src/scm/webid-oidc/errors.scm:1285
 #, scheme-format
 msgid "the key ~s does not hash to ~a"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1271
+#: src/scm/webid-oidc/errors.scm:1287
 #, scheme-format
 msgid "the key confirmation of ~s failed (because ~a)"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1273
+#: src/scm/webid-oidc/errors.scm:1289
 #, scheme-format
 msgid "the key confirmation of ~s failed"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1275
+#: src/scm/webid-oidc/errors.scm:1291
 #, scheme-format
 msgid "the jti ~s has already been found (because ~a)"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1278
+#: src/scm/webid-oidc/errors.scm:1294
 #, scheme-format
 msgid "I cannot decode ~s as an access token (because ~a)"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1281
+#: src/scm/webid-oidc/errors.scm:1297
 #, scheme-format
 msgid "I cannot encode ~s as an access token with key ~s (because ~a)"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1284
+#: src/scm/webid-oidc/errors.scm:1300
 #, scheme-format
 msgid "I cannot decode ~s as a DPoP proof (because ~a)"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1287
+#: src/scm/webid-oidc/errors.scm:1303
 #, scheme-format
 msgid "I cannot encode ~s as a DPoP proof (because ~a)"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1290
+#: src/scm/webid-oidc/errors.scm:1306
 #, scheme-format
 msgid "I could not fetch a RDF graph at ~a (because ~a)"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1293
+#: src/scm/webid-oidc/errors.scm:1309
 #, scheme-format
 msgid "~s is not a client manifest (because ~a)"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1296
+#: src/scm/webid-oidc/errors.scm:1312
 #, scheme-format
 msgid "~s does not authorize redirection URI ~a"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1299
+#: src/scm/webid-oidc/errors.scm:1315
 msgid "I cannot serve a public manifest"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1301
+#: src/scm/webid-oidc/errors.scm:1317
 #, scheme-format
 msgid "~a does not have a client manifest registration triple"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1304
+#: src/scm/webid-oidc/errors.scm:1320
 #, scheme-format
 msgid "the client manifest at ~a is advertised for ~a"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1307
+#: src/scm/webid-oidc/errors.scm:1323
 #, scheme-format
 msgid "I could not fetch the client manifest of ~a (because ~a)"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1310
+#: src/scm/webid-oidc/errors.scm:1326
 #, scheme-format
 msgid "~s is not an authorization code (because ~a)"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1313
+#: src/scm/webid-oidc/errors.scm:1329
 #, scheme-format
 msgid "~s is not an authorization code header (because ~a)"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1316
+#: src/scm/webid-oidc/errors.scm:1332
 #, scheme-format
 msgid "~s is not an authorization code payload (because ~a)"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1319
+#: src/scm/webid-oidc/errors.scm:1335
 #, scheme-format
 msgid "the current time is ~a, and the authorization code expired at ~a"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1323
+#: src/scm/webid-oidc/errors.scm:1339
 #, scheme-format
 msgid "I cannot decode ~s as an authorization code (because ~a)"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1326
+#: src/scm/webid-oidc/errors.scm:1342
 #, scheme-format
 msgid "I cannot encode ~s as an authorization code (because ~a)"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1329
+#: src/scm/webid-oidc/errors.scm:1345
 #, scheme-format
 msgid "there is no such refresh token as ~s"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1332
+#: src/scm/webid-oidc/errors.scm:1348
 #, scheme-format
 msgid ""
 "the refresh token is bound to a key confirmed as ~s, but it is used with key "
 "~s"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1335
+#: src/scm/webid-oidc/errors.scm:1351
 #, scheme-format
 msgid "I cannot decode ~s as an ID token (because ~a)"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1338
+#: src/scm/webid-oidc/errors.scm:1354
 #, scheme-format
 msgid "I cannot encode ~s as an ID token (because ~a)"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1341
+#: src/scm/webid-oidc/errors.scm:1357
 #, scheme-format
 msgid "the grant type ~s is not supported"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1344
+#: src/scm/webid-oidc/errors.scm:1360
 msgid "there is no authorization code in the request"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1346
+#: src/scm/webid-oidc/errors.scm:1362
 msgid "there is no refresh token in the request"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1348
+#: src/scm/webid-oidc/errors.scm:1364
 #, scheme-format
 msgid "~s is not an ID token (because ~a)"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1351
+#: src/scm/webid-oidc/errors.scm:1367
 #, scheme-format
 msgid "~s is not an ID token header (because ~a)"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1354
+#: src/scm/webid-oidc/errors.scm:1370
 #, scheme-format
 msgid "~s is not an ID token payload (because ~a)"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1357
+#: src/scm/webid-oidc/errors.scm:1373
 #, scheme-format
 msgid ""
 "I couldn’t set the locale to ~s as an approximation of the client locale ~s"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1360
+#: src/scm/webid-oidc/errors.scm:1376
 #, scheme-format
 msgid "~s does not admit ~s as an identity provider"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1363
+#: src/scm/webid-oidc/errors.scm:1379
 #, scheme-format
 msgid ""
 "~a is neither an identity provider (because ~a) nor a webid (because ~a)"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1368
+#: src/scm/webid-oidc/errors.scm:1384
 #, scheme-format
 msgid "the token request failed (because ~a)"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1371
+#: src/scm/webid-oidc/errors.scm:1387
 #, scheme-format
 msgid "you don’t have a refresh token for identity ~a certified by ~a in ~s"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1376
+#: src/scm/webid-oidc/errors.scm:1392
 #, scheme-format
 msgid "all identity provider candidates for ~a failed: ~a"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1380
+#: src/scm/webid-oidc/errors.scm:1396
 #, scheme-format
 msgid "~s failed (because ~a)"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1383
+#: src/scm/webid-oidc/errors.scm:1399
 msgid ", "
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1385
+#: src/scm/webid-oidc/errors.scm:1401
 #, scheme-format
 msgid "no resource has been found to serve URI path ~s"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1388
+#: src/scm/webid-oidc/errors.scm:1404
 #, scheme-format
 msgid "the resource kind ~s is absent for the resource at ~s"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1391
+#: src/scm/webid-oidc/errors.scm:1407
 #, scheme-format
 msgid "no resource has been found to serve URI path ~s, but ~s exists"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1394
+#: src/scm/webid-oidc/errors.scm:1410
 msgid "the root storage cannot be deleted"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1396
+#: src/scm/webid-oidc/errors.scm:1412
 #, scheme-format
 msgid "the container ~s should be emptied before being deleted"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1399
+#: src/scm/webid-oidc/errors.scm:1415
 #, scheme-format
 msgid "the group ~s cannot be fetched (because ~a)"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1403
+#: src/scm/webid-oidc/errors.scm:1419
 #, scheme-format
 msgid "the containment triples in the request to update ~s are not up to date"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1406
+#: src/scm/webid-oidc/errors.scm:1422
 #, scheme-format
 msgid "the server cannot process resources with the ~s content-type"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1409
+#: src/scm/webid-oidc/errors.scm:1425
 #, scheme-format
 msgid ""
 "the client wants to create a resource at ~s, which is reserved for an "
 "auxiliary resource"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1412
+#: src/scm/webid-oidc/errors.scm:1428
 #, scheme-format
 msgid ""
 "the operation on ~s by ~a is refused, because it’s not by ~s and the access "
 "control forbids the following mode of operation: ~s"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1416
+#: src/scm/webid-oidc/errors.scm:1432
 msgid "an anonymous user"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1421
+#: src/scm/webid-oidc/errors.scm:1437
 #, scheme-format
 msgid ""
 "the client precondition failed for ~s: it allows for ~s, forbids ~s, but the "
 "resource has a representation of ~s"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1423
+#: src/scm/webid-oidc/errors.scm:1439
 #, scheme-format
 msgid ""
 "the client precondition failed for ~s: it allows for ~s, forbids ~s, but the "
 "resource has no representation"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1428
+#: src/scm/webid-oidc/errors.scm:1442
+#, scheme-format
+msgid ""
+"the client wanted a response with a content type among ~s, but the resource "
+"at ~s has content-type ~s which cannot be converted to one of them"
+msgstr ""
+
+#: src/scm/webid-oidc/errors.scm:1449
 msgid "that’s it"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1432
+#: src/scm/webid-oidc/errors.scm:1453
 #, scheme-format
 msgid "~a and ~a"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1435
+#: src/scm/webid-oidc/errors.scm:1456
 #, scheme-format
 msgid "~a, ~a"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1439
+#: src/scm/webid-oidc/errors.scm:1460
 #, scheme-format
 msgid "the signature ~a does not match key ~s with payload ~a"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1442
+#: src/scm/webid-oidc/errors.scm:1463
 msgid "there is an undefined variable"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1444
+#: src/scm/webid-oidc/errors.scm:1465
 #, scheme-format
 msgid "the origin is ~a"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1447
+#: src/scm/webid-oidc/errors.scm:1468
 #, scheme-format
 msgid "a message is attached: ~a"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1450
+#: src/scm/webid-oidc/errors.scm:1471
 #, scheme-format
 msgid "the values ~s are problematic"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1453
+#: src/scm/webid-oidc/errors.scm:1474
 #, scheme-format
 msgid "there is a kind (~s) and args ~s"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1456
+#: src/scm/webid-oidc/errors.scm:1477
 msgid "there is an assertion failure"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1458
+#: src/scm/webid-oidc/errors.scm:1479
 #, scheme-format
 msgid "the program quits with code ~a"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1461
+#: src/scm/webid-oidc/errors.scm:1482
 msgid "the program cannot recover from this exception"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1463
+#: src/scm/webid-oidc/errors.scm:1484
 msgid "there is an external error"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1465
+#: src/scm/webid-oidc/errors.scm:1486
 msgid "there is an error"
 msgstr ""
 
-#: src/scm/webid-oidc/errors.scm:1467
+#: src/scm/webid-oidc/errors.scm:1488
 #, scheme-format
 msgid "Unhandled exception type ~a."
 msgstr ""
@@ -927,17 +934,17 @@ msgid ""
 "permissions."
 msgstr ""
 
-#: src/scm/webid-oidc/resource-server.scm:91
+#: src/scm/webid-oidc/resource-server.scm:92
 #, scheme-format
 msgid "~a: authentication failure: ~a\n"
 msgstr ""
 
-#: src/scm/webid-oidc/resource-server.scm:220
+#: src/scm/webid-oidc/resource-server.scm:237
 #, scheme-format
 msgid "Warning: ~a\n"
 msgstr ""
 
-#: src/scm/webid-oidc/resource-server.scm:223
+#: src/scm/webid-oidc/resource-server.scm:240
 #, scheme-format
 msgid "Error: ~a\n"
 msgstr ""
diff --git a/src/scm/webid-oidc/Makefile.am b/src/scm/webid-oidc/Makefile.am
index 867d2ee..bdb3af8 100644
--- a/src/scm/webid-oidc/Makefile.am
+++ b/src/scm/webid-oidc/Makefile.am
@@ -26,6 +26,7 @@ dist_webidoidcmod_DATA += \
   %reldir%/jti.scm \
   %reldir%/dpop-proof.scm \
   %reldir%/fetch.scm \
+  %reldir%/serve.scm \
   %reldir%/client-manifest.scm \
   %reldir%/authorization-code.scm \
   %reldir%/refresh-token.scm \
@@ -57,6 +58,7 @@ webidoidcgo_DATA += \
   %reldir%/jti.go \
   %reldir%/dpop-proof.go \
   %reldir%/fetch.go \
+  %reldir%/serve.go \
   %reldir%/client-manifest.go \
   %reldir%/authorization-code.go \
   %reldir%/refresh-token.go \
diff --git a/src/scm/webid-oidc/errors.scm b/src/scm/webid-oidc/errors.scm
index c969a40..522e563 100644
--- a/src/scm/webid-oidc/errors.scm
+++ b/src/scm/webid-oidc/errors.scm
@@ -1036,6 +1036,22 @@
         precondition-failed-if-none-match
         precondition-failed-real-etag)
 
+(define-exception-type
+  &not-acceptable
+  &external-error
+  make-not-acceptable
+  not-acceptable?
+  (client-accepts not-acceptable-client-accepts)
+  (path not-acceptable-path)
+  (content-type not-acceptable-content-type))
+
+(export &not-acceptable
+        make-not-acceptable
+        not-acceptable?
+        not-acceptable-client-accepts
+        not-acceptable-path
+        not-acceptable-content-type)
+
 (define*-public (error->str err #:key (max-depth #f))
   (if (record? err)
       (let* ((type (record-type-descriptor err))
@@ -1422,6 +1438,11 @@
                        (get 'path) (get 'if-match) (get 'if-none-match) (get 'real-etag))
                (format #f (G_ "the client precondition failed for ~s: it allows for ~s, forbids ~s, but the resource has no representation")
                        (get 'path) (get 'if-match) (get 'if-none-match))))
+          ((&not-acceptable)
+           (format #f (G_ "the client wanted a response with a content type among ~s, but the resource at ~s has content-type ~s which cannot be converted to one of them")
+                   (get 'client-accepts)
+                   (get 'path)
+                   (get 'content-type)))
           ((&compound-exception)
            (let ((components (get 'components)))
              (if (null? components)
diff --git a/src/scm/webid-oidc/resource-server.scm b/src/scm/webid-oidc/resource-server.scm
index 9988cba..7f9c8f9 100644
--- a/src/scm/webid-oidc/resource-server.scm
+++ b/src/scm/webid-oidc/resource-server.scm
@@ -20,6 +20,7 @@
   #:use-module (webid-oidc provider-confirmation)
   #:use-module (webid-oidc jwk)
   #:use-module (webid-oidc dpop-proof)
+  #:use-module (webid-oidc serve)
   #:use-module (webid-oidc server create)
   #:use-module (webid-oidc server read)
   #:use-module (webid-oidc server update)
@@ -148,12 +149,27 @@
                         #:http-get http-get)
                 (with-exception-handler
                     (lambda (error)
-                      (return
-                       (build-response
-                        #:headers headers)
-                       (if (eq? method 'GET)
-                           content
-                           "")))
+                      (let ((true-content-type
+                             (car (assq-ref headers 'content-type)))
+                            (other-headers
+                             (filter
+                              (lambda (h)
+                                (not (eq? (car h) 'content-type)))
+                              headers)))
+                        (receive (negociated-content-type
+                                  negociated-content)
+                            (convert (request-accept request #f)
+                                     server-uri
+                                     (uri-path (request-uri request))
+                                     true-content-type
+                                     content)
+                          (return
+                           (build-response
+                            #:headers (cons `(content-type ,negociated-content-type)
+                                            other-headers))
+                           (if (eq? method 'GET)
+                               negociated-content
+                               "")))))
                   (lambda ()
                     (unless (or (request-if-match request)
                                 (request-if-none-match request))
@@ -220,59 +236,64 @@
          (if (cannot-fetch-group? error)
              (format (current-error-port) (G_ "Warning: ~a\n")
                      (error->str error))
-             (begin
-               (format (current-error-port) (G_ "Error: ~a\n")
-                       (error->str error))
-               (cond
-                ((uri-slash-semantics-error? error)
-                 (return
-                  (build-response
-                   #:code 301
-                   #:reason-phrase "Found"
-                   #:headers
-                   `((location
-                      . ,(build-uri
-                          (uri-scheme server-uri)
-                          #:userinfo (uri-userinfo server-uri)
-                          #:host (uri-host server-uri)
-                          #:port (uri-port server-uri)
-                          #:path (uri-slash-semantics-error-expected-path error)))))
-                  ""))
-                ((or (path-not-found? error)
-                     (auxiliary-resource-absent? error)
-                     (forbidden? error))
-                 (if user
-                     ;; That’s a forbidden
-                     (return
-                      (build-response #:code 403 #:reason-phrase "Forbidden")
-                      "")
-                     (return
-                      (build-response #:code 401 #:reason-phrase "Unauthorized"
-                                      #:headers `((www-authenticate . ((DPoP)))))
-                      "")))
-                ((or (cannot-delete-root? error))
-                 (return
-                  (build-response
-                   #:code 405
-                   #:reason-phrase "Method Not Allowed")
-                  ""))
-                ((or (container-not-empty? error)
-                     (incorrect-containment-triples? error)
-                     (path-is-auxiliary? error))
-                 (return
-                  (build-response
-                   #:code 409
-                   #:reason-phrase "Conflict")
-                  ""))
-                ((unsupported-media-type? error)
-                 (return
-                  (build-response
-                   #:code 415
-                   #:reason-phrase "Unsupported Media Type")
-                  ""))
-                ((precondition-failed? error)
-                 (return
-                  (build-response
-                   #:code 412
-                   #:reason-phrase "Precondition Failed")
-                  ""))))))))))
+             (cond
+              ((uri-slash-semantics-error? error)
+               (return
+                (build-response
+                 #:code 301
+                 #:reason-phrase "Found"
+                 #:headers
+                 `((location
+                    . ,(build-uri
+                        (uri-scheme server-uri)
+                        #:userinfo (uri-userinfo server-uri)
+                        #:host (uri-host server-uri)
+                        #:port (uri-port server-uri)
+                        #:path (uri-slash-semantics-error-expected-path error)))))
+                #f))
+              ((or (path-not-found? error)
+                   (auxiliary-resource-absent? error)
+                   (forbidden? error))
+               (if user
+                   ;; That’s a forbidden
+                   (return
+                    (build-response #:code 403 #:reason-phrase "Forbidden")
+                    #f)
+                   (return
+                    (build-response #:code 401 #:reason-phrase "Unauthorized"
+                                    #:headers `((www-authenticate . ((DPoP)))))
+                    #f)))
+              ((or (cannot-delete-root? error))
+               (return
+                (build-response
+                 #:code 405
+                 #:reason-phrase "Method Not Allowed")
+                #f))
+              ((or (container-not-empty? error)
+                   (incorrect-containment-triples? error)
+                   (path-is-auxiliary? error))
+               (return
+                (build-response
+                 #:code 409
+                 #:reason-phrase "Conflict")
+                #f))
+              ((unsupported-media-type? error)
+               (return
+                (build-response
+                 #:code 415
+                 #:reason-phrase "Unsupported Media Type")
+                #f))
+              ((precondition-failed? error)
+               (return
+                (build-response
+                 #:code 412
+                 #:reason-phrase "Precondition Failed")
+                #f))
+              ((not-acceptable? error)
+               (return
+                (build-response
+                 #:code 406
+                 #:reason-phrase "Not Acceptable")
+                #f))
+              (else
+               (raise-exception error)))))))))
diff --git a/src/scm/webid-oidc/serve.scm b/src/scm/webid-oidc/serve.scm
new file mode 100644
index 0000000..4f54495
--- /dev/null
+++ b/src/scm/webid-oidc/serve.scm
@@ -0,0 +1,73 @@
+;; webid-oidc, implementation of the Solid specification
+;; Copyright (C) 2021  Vivien Kraus
+
+;; This program is free software: you can redistribute it and/or modify
+;; it under the terms of the GNU Affero General Public License as
+;; published by the Free Software Foundation, either version 3 of the
+;; License, or (at your option) any later version.
+
+;; This program is distributed in the hope that it will be useful,
+;; but WITHOUT ANY WARRANTY; without even the implied warranty of
+;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;; GNU Affero General Public License for more details.
+
+;; You should have received a copy of the GNU Affero General Public License
+;; along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+(define-module (webid-oidc serve)
+  #:use-module (webid-oidc errors)
+  #:use-module (webid-oidc fetch)
+  #:use-module (ice-9 optargs)
+  #:use-module (ice-9 receive)
+  #:use-module (ice-9 exceptions)
+  #:use-module (rnrs bytevectors)
+  #:use-module (web client)
+  #:use-module (web request)
+  #:use-module (web response)
+  #:use-module (web uri)
+  #:use-module (rdf rdf)
+  #:use-module (turtle fromrdf)
+  #:use-module (nquads fromrdf)
+  #:export
+  (
+   convert
+   ))
+
+(define (convert client-accepts server-name path content-type content)
+  (let ((data-as-rdf
+         (false-if-exception
+          (fetch
+           (build-uri (uri-scheme server-name)
+                      #:userinfo (uri-userinfo server-name)
+                      #:host (uri-host server-name)
+                      #:port (uri-port server-name)
+                      #:path path)
+           #:http-get
+           (lambda args
+             (values (build-response
+                      #:headers `((content-type ,content-type)))
+                     content))))))
+    (if client-accepts
+        ;; Content negociation is asked
+        (let try-satisfy ((accepts client-accepts))
+          (if (null? accepts)
+              (raise-exception (make-not-acceptable client-accepts path content-type))
+              (let ((request (caar accepts)))
+                (cond
+                 ((or (eq? request content-type)
+                      (eq? request '*/*))
+                  (values content-type content))
+                 ((and (eq? request 'text/turtle) data-as-rdf)
+                  (values 'text/turtle
+                          (rdf->turtle data-as-rdf)))
+                 ((and (or (eq? request 'application/n-quads)
+                           (eq? request 'text/x-nquads))
+                       data-as-rdf)
+                  (values request
+                          (rdf->nquads
+                           (make-rdf-dataset data-as-rdf '()))))
+                 ;; Add other conversion strategies here
+                 (else
+                  (try-satisfy (cdr accepts)))))))
+        ;; Content negociation is unwanted
+        (values content-type content))))