Don't throw exception for token error response. (#844)

* Don't throw exception for token error response.

src/oic/oauth2/__init__.py

@@ -743,14 +743,9 @@ def parse_request_response(
             logger.error("(%d) %s" % (reqresp.status_code, sanitize(reqresp.text)))
             raise ParseError("ERROR: Something went wrong: %s" % reqresp.text)
 
-        if reqresp.status_code in SUCCESSFUL:
-            verified_body_type = verify_header(reqresp, body_type)
-        elif (
-            reqresp.status_code in [400, 401]
-            and response
-            and issubclass(response, ErrorResponse)
+        if reqresp.status_code in SUCCESSFUL or (
+            reqresp.status_code in [400, 401] and response
         ):
-            # This is okay if we are expecting an error response, do not log
             verified_body_type = verify_header(reqresp, body_type)
         else:
             # Any other error

tests/test_oauth2.py

@@ -11,6 +11,7 @@
 from oic.oauth2 import Grant
 from oic.oauth2 import Server
 from oic.oauth2 import Token
+from oic.oauth2 import TokenErrorResponse
 from oic.oauth2.exception import GrantError
 from oic.oauth2.exception import MissingEndpoint
 from oic.oauth2.exception import ResponseError
@@ -598,6 +599,27 @@ class CCMessageFactory(OauthMessageFactory):
         assert isinstance(resp, AccessTokenResponse)
         assert resp["access_token"] == "Token"
 
+    def test_do_access_token_request_handle_error_response(self):
+        class CCMessageFactory(OauthMessageFactory):
+            """We are doing client credentials."""
+
+            token_endpoint = MessageTuple(CCAccessTokenRequest, AccessTokenResponse)
+
+        self.client.message_factory = CCMessageFactory
+        with responses.RequestsMock() as rsps:
+            rsps.add(
+                rsps.POST,
+                self.token_endpoint,
+                status=400,
+                json={"error": "invalid_request", "error_description": "test error"},
+            )
+
+            resp = self.client.do_access_token_request()
+            assert rsps.calls[0].request.body == "grant_type=client_credentials"
+
+        assert isinstance(resp, TokenErrorResponse)
+        assert resp["error"] == "invalid_request"
+
     def test_do_access_token_request_extension_grant(self):
         class ExtensionMessageFactory(OauthMessageFactory):
             """We are doing Extension grant."""