diff --git a/example/flask_op/views.py b/example/flask_op/views.py
index 648c3de..1852881 100644
--- a/example/flask_op/views.py
+++ b/example/flask_op/views.py
@@ -18,8 +18,8 @@
 import werkzeug
 
 from oidcop.exception import FailedAuthentication
-from oidcop.exception import InvalidClient
-from oidcop.exception import UnknownClient
+from oidcop.exception import ClientAuthenticationError
+from oidcop.exception import TokenAuthenticationError
 from oidcop.oidc.token import Token
 
 # logger = logging.getLogger(__name__)
@@ -224,12 +224,18 @@ def service_endpoint(endpoint):
     if request.method == 'GET':
         try:
             req_args = endpoint.parse_request(request.args.to_dict(), http_info=http_info)
-        except (InvalidClient, UnknownClient) as err:
+        except ClientAuthenticationError as err:
             _log.error(err)
             return make_response(json.dumps({
                 'error': 'unauthorized_client',
                 'error_description': str(err)
-            }), 400)
+            }), 401)
+        except TokenAuthenticationError as err:
+            _log.error(err)
+            return make_response(json.dumps({
+                'error': 'invalid_token',
+                'error_description': str(err)
+            }), 401)
         except Exception as err:
             _log.error(err)
             return make_response(json.dumps({
diff --git a/src/oidcop/client_authn.py b/src/oidcop/client_authn.py
index 8c540b0..a34e632 100755
--- a/src/oidcop/client_authn.py
+++ b/src/oidcop/client_authn.py
@@ -19,6 +19,7 @@
 from oidcop import JWT_BEARER
 from oidcop import sanitize
 from oidcop.endpoint_context import EndpointContext
+from oidcop.exception import BearerTokenAuthenticationError
 from oidcop.exception import InvalidClient
 from oidcop.exception import MultipleUsage
 from oidcop.exception import NotForMe
@@ -406,15 +407,15 @@ def verify_client(
     elif not client_id and get_client_id_from_token:
         if not _token:
             logger.warning("No token")
-            raise ValueError("No token")
+            raise BearerTokenAuthenticationError("No token")
 
         try:
             # get_client_id_from_token is a callback... Do not abuse for code readability.
             auth_info["client_id"] = get_client_id_from_token(endpoint_context, _token, request)
         except ToOld:
-            raise ValueError("Expired token")
+            raise BearerTokenAuthenticationError("Expired token")
         except KeyError:
-            raise ValueError("Unknown token")
+            raise BearerTokenAuthenticationError("Unknown token")
 
     return auth_info
 
diff --git a/src/oidcop/endpoint.py b/src/oidcop/endpoint.py
index 2b98815..369940b 100755
--- a/src/oidcop/endpoint.py
+++ b/src/oidcop/endpoint.py
@@ -175,7 +175,6 @@ def parse_request(
             req = self.request_cls()
 
         # Verify that the client is allowed to do this
-        _client_id = ""
         auth_info = self.client_authentication(req, http_info, endpoint=self, **kwargs)
 
         if "client_id" in auth_info:
@@ -206,14 +205,6 @@ def parse_request(
             request=req, client_id=_client_id, http_info=http_info, **kwargs
         )
 
-    def get_client_id_from_token(
-        self,
-        endpoint_context: EndpointContext,
-        token: str,
-        request: Optional[Union[Message, dict]] = None,
-    ):
-        return ""
-
     def client_authentication(self, request: Message, http_info: Optional[dict] = None, **kwargs):
         """
         Do client authentication
@@ -230,7 +221,7 @@ def client_authentication(self, request: Message, http_info: Optional[dict] = No
             endpoint_context=self.server_get("endpoint_context"),
             request=request,
             http_info=http_info,
-            get_client_id_from_token=self.get_client_id_from_token,
+            get_client_id_from_token=getattr(self, "get_client_id_from_token", None),
             **kwargs
         )
 
diff --git a/src/oidcop/exception.py b/src/oidcop/exception.py
index fcbe4b2..eb500cf 100755
--- a/src/oidcop/exception.py
+++ b/src/oidcop/exception.py
@@ -58,15 +58,23 @@ class RedirectURIError(OidcEndpointError):
     pass
 
 
-class UnknownClient(OidcEndpointError):
+class ClientAuthenticationError(OidcEndpointError):
     pass
 
 
-class InvalidClient(OidcEndpointError):
+class UnknownClient(ClientAuthenticationError):
     pass
 
 
-class UnAuthorizedClient(OidcEndpointError):
+class InvalidClient(ClientAuthenticationError):
+    pass
+
+
+class UnAuthorizedClient(ClientAuthenticationError):
+    pass
+
+
+class BearerTokenAuthenticationError(OidcEndpointError):
     pass
 
 
diff --git a/tests/test_26_oidc_userinfo_endpoint.py b/tests/test_26_oidc_userinfo_endpoint.py
index 5c6a633..3ed37cc 100755
--- a/tests/test_26_oidc_userinfo_endpoint.py
+++ b/tests/test_26_oidc_userinfo_endpoint.py
@@ -12,6 +12,7 @@
 from oidcop.configure import OPConfiguration
 from oidcop.cookie_handler import CookieHandler
 from oidcop.exception import ImproperlyConfigured
+from oidcop.exception import BearerTokenAuthenticationError
 from oidcop.oidc import userinfo
 from oidcop.oidc.authorization import Authorization
 from oidcop.oidc.provider_config import ProviderConfiguration
@@ -513,11 +514,8 @@ def mock():
 
         monkeypatch.setattr("oidcop.token.utc_time_sans_frac", mock)
 
-        _req = self.endpoint.parse_request({}, http_info=http_info)
-
-        assert _req.to_dict() == {
-            "error": "invalid_token", "error_description": "Expired token"
-        }
+        with pytest.raises(BearerTokenAuthenticationError):
+            self.endpoint.parse_request({}, http_info=http_info)
 
     def test_userinfo_claims(self):
         _acr = "https://refeds.org/profile/mfa"