Check if PKCE is supported when exchanging token

src/oidcc_token.erl

@@ -230,6 +230,7 @@ See https://datatracker.ietf.org/doc/html/rfc6749#section-4.1.3.
     | {invalid_property, {
         Field :: id_token | refresh_token | access_token | expires_in | scopes, GivenValue :: term()
     }}
+    | no_supported_code_challenge
     | oidcc_jwt_util:error()
     | oidcc_http_util:error().
 
@@ -359,7 +360,6 @@ retrieve(AuthCode, ClientContext, Opts) ->
 
     case lists:member(<<"authorization_code">>, GrantTypesSupported) of
         true ->
-            PkceVerifier = maps:get(pkce_verifier, Opts, none),
             QsBody =
                 [
                     {<<"grant_type">>, <<"authorization_code">>},
@@ -375,7 +375,7 @@ retrieve(AuthCode, ClientContext, Opts) ->
             maybe
                 {ok, Token} ?=
                     retrieve_a_token(
-                        QsBody, PkceVerifier, ClientContext, Opts, TelemetryOpts, true
+                        QsBody, ClientContext, Opts, TelemetryOpts, true
                     ),
                 extract_response(Token, ClientContext, Opts)
             end;
@@ -535,7 +535,7 @@ refresh(RefreshToken, ClientContext, Opts) ->
 
             maybe
                 {ok, Token} ?=
-                    retrieve_a_token(QueryString1, none, ClientContext, Opts, TelemetryOpts, true),
+                    retrieve_a_token(QueryString1, ClientContext, Opts, TelemetryOpts, true),
                 {ok, TokenRecord} ?=
                     extract_response(Token, ClientContext, maps:put(nonce, any, Opts)),
                 case TokenRecord of
@@ -631,7 +631,7 @@ jwt_profile(Subject, ClientContext, Jwk, Opts) ->
 
             maybe
                 {ok, Token} ?=
-                    retrieve_a_token(QueryString1, none, ClientContext, Opts, TelemetryOpts, false),
+                    retrieve_a_token(QueryString1, ClientContext, Opts, TelemetryOpts, false),
                 {ok, TokenRecord} ?=
                     extract_response(Token, ClientContext, maps:put(nonce, any, Opts)),
                 case TokenRecord of
@@ -692,7 +692,7 @@ client_credentials(ClientContext, Opts) ->
 
             maybe
                 {ok, Token} ?=
-                    retrieve_a_token(QueryString1, none, ClientContext, Opts, TelemetryOpts, true),
+                    retrieve_a_token(QueryString1, ClientContext, Opts, TelemetryOpts, true),
                 extract_response(Token, ClientContext, maps:put(nonce, any, Opts))
             end;
         false ->
@@ -1139,21 +1139,16 @@ verify_missing_required_claims(Claims) ->
     end.
 
 -spec retrieve_a_token(
-    QsBodyIn, PkceVerifier, ClientContext, Opts, TelemetryOpts, AuthenticateClient
+    QsBodyIn, ClientContext, Opts, TelemetryOpts, AuthenticateClient
 ) ->
     {ok, map()} | {error, error()}
 when
     QsBodyIn :: oidcc_http_util:query_params(),
-    PkceVerifier :: binary() | none,
     ClientContext :: oidcc_client_context:t(),
     Opts :: retrieve_opts() | refresh_opts(),
     TelemetryOpts :: oidcc_http_util:telemetry_opts(),
     AuthenticateClient :: boolean().
-retrieve_a_token(
-    _QsBodyIn, none, _ClientContext, #{require_pkce := true}, _TelemetryOpts, _AuthenticateClient
-) ->
-    {error, pkce_verifier_required};
-retrieve_a_token(QsBodyIn, PkceVerifier, ClientContext, Opts, TelemetryOpts, AuthenticateClient) ->
+retrieve_a_token(QsBodyIn, ClientContext, Opts, TelemetryOpts, AuthenticateClient) ->
     #oidcc_client_context{provider_configuration = Configuration} =
         ClientContext,
     #oidcc_provider_configuration{
@@ -1168,7 +1163,6 @@ retrieve_a_token(QsBodyIn, PkceVerifier, ClientContext, Opts, TelemetryOpts, Aut
     Header0 = [{"accept", "application/jwt, application/json"}],
 
     QsBody0 = QsBodyIn ++ maps:get(body_extension, Opts, []),
-    QsBody = add_pkce_verifier(QsBody0, PkceVerifier),
 
     SupportedAuthMethods =
         case AuthenticateClient of
@@ -1184,6 +1178,7 @@ retrieve_a_token(QsBodyIn, PkceVerifier, ClientContext, Opts, TelemetryOpts, Aut
                 #{}
         end,
     maybe
+        {ok, QsBody} ?= add_pkce_verifier(QsBody0, Opts, ClientContext),
         {ok, {Body, Header1}, AuthMethod} ?=
             oidcc_auth_util:add_client_authentication(
                 QsBody, Header0, SupportedAuthMethods, SigningAlgs, Opts, ClientContext
@@ -1211,7 +1206,6 @@ retrieve_a_token(QsBodyIn, PkceVerifier, ClientContext, Opts, TelemetryOpts, Aut
             %% (to avoid infinite loops)
             retrieve_a_token(
                 QsBodyIn,
-                PkceVerifier,
                 ClientContext,
                 Opts#{dpop_nonce => NewDpopNonce},
                 TelemetryOpts,
@@ -1221,10 +1215,37 @@ retrieve_a_token(QsBodyIn, PkceVerifier, ClientContext, Opts, TelemetryOpts, Aut
             {error, Reason}
     end.
 
--spec add_pkce_verifier(QueryList, PkceVerifier) -> oidcc_http_util:query_params() when
+-spec add_pkce_verifier(QueryList, Opts, ClientContext) ->
+    {ok, oidcc_http_util:query_params()} | {error, error()}
+when
     QueryList :: oidcc_http_util:query_params(),
-    PkceVerifier :: binary() | none.
-add_pkce_verifier(BodyQs, none) ->
-    BodyQs;
-add_pkce_verifier(BodyQs, PkceVerifier) ->
-    [{<<"code_verifier">>, PkceVerifier} | BodyQs].
+    Opts :: retrieve_opts() | refresh_opts(),
+    ClientContext :: oidcc_client_context:t().
+add_pkce_verifier(BodyQs, #{pkce_verifier := PkceVerifier} = Opts, ClientContext) ->
+    #oidcc_client_context{provider_configuration = ProviderConfiguration} = ClientContext,
+    #oidcc_provider_configuration{code_challenge_methods_supported = CodeChallengeMethodsSupported} =
+        ProviderConfiguration,
+    RequirePkce = maps:get(require_pkce, Opts, false),
+
+    case CodeChallengeMethodsSupported of
+        undefined when RequirePkce =:= true ->
+            {error, no_supported_code_challenge};
+        undefined ->
+            {ok, BodyQs};
+        Methods when is_list(Methods) ->
+            case
+                lists:member(<<"S256">>, CodeChallengeMethodsSupported) or
+                    lists:member(<<"plain">>, CodeChallengeMethodsSupported)
+            of
+                true ->
+                    {ok, [{<<"code_verifier">>, PkceVerifier} | BodyQs]};
+                false when RequirePkce =:= true ->
+                    {error, no_supported_code_challenge};
+                false ->
+                    {ok, BodyQs}
+            end
+    end;
+add_pkce_verifier(_BodyQs, #{require_pkce := true}, _ClientContext) ->
+    {error, pkce_verifier_required};
+add_pkce_verifier(BodyQs, _Opts, _ClientContext) ->
+    {ok, BodyQs}.

test/oidcc_token_test.erl

@@ -1710,18 +1710,66 @@ trusted_audiences_test() ->
 
     ok.
 
-retrieve_pkce_required_test() ->
-    ClientContext = client_context_fapi2_fixture(),
+retrieve_pkce_test() ->
+    ok = meck:new(httpc, [no_link]),
+    HttpFun =
+        fun(
+            post,
+            {_TokenEndpoint, _Header, "application/x-www-form-urlencoded", _Body},
+            _HttpOpts,
+            _Opts,
+            _Profile
+        ) ->
+            {ok, {{"HTTP/1.1", 500, "Server Error"}, [], "SUCCESS"}}
+        end,
+    ok = meck:expect(httpc, request, HttpFun),
+
+    PkceSupportedClientContext = client_context_fapi2_fixture(),
+    PkceUnsupportedClientContext = PkceSupportedClientContext#oidcc_client_context{
+        provider_configuration = PkceSupportedClientContext#oidcc_client_context.provider_configuration#oidcc_provider_configuration{
+            code_challenge_methods_supported = undefined
+        }
+    },
     RedirectUri = <<"https://redirect.example/">>,
 
     ?assertEqual(
         {error, pkce_verifier_required},
-        oidcc_token:retrieve(<<"code">>, ClientContext, #{
+        oidcc_token:retrieve(<<"code">>, PkceSupportedClientContext, #{
             redirect_uri => RedirectUri,
             require_pkce => true
         })
     ),
 
+    ?assertEqual(
+        {error, {http_error, 500, "SUCCESS"}},
+        oidcc_token:retrieve(<<"code">>, PkceSupportedClientContext, #{
+            redirect_uri => RedirectUri,
+            require_pkce => true,
+            pkce_verifier => <<"verifier">>
+        })
+    ),
+
+    ?assertEqual(
+        {error, no_supported_code_challenge},
+        oidcc_token:retrieve(<<"code">>, PkceUnsupportedClientContext, #{
+            redirect_uri => RedirectUri,
+            require_pkce => true,
+            pkce_verifier => <<"verifier">>
+        })
+    ),
+
+    ?assertEqual(
+        {error, {http_error, 500, "SUCCESS"}},
+        oidcc_token:retrieve(<<"code">>, PkceUnsupportedClientContext, #{
+            redirect_uri => RedirectUri,
+            pkce_verifier => <<"verifier">>
+        })
+    ),
+
+    true = meck:validate(httpc),
+
+    meck:unload(httpc),
+
     ok.
 
 validate_jarm_test() ->