diff --git a/src/oidcendpoint/exception.py b/src/oidcendpoint/exception.py
index dfe0114..8ab680d 100755
--- a/src/oidcendpoint/exception.py
+++ b/src/oidcendpoint/exception.py
@@ -66,6 +66,10 @@ class UnAuthorizedClient(OidcEndpointError):
     pass
 
 
+class UnAuthorizedClientScope(OidcEndpointError):
+    pass
+
+
 class InvalidCookieSign(Exception):
     pass
 
diff --git a/src/oidcendpoint/oauth2/authorization.py b/src/oidcendpoint/oauth2/authorization.py
index fd662e3..000d881 100755
--- a/src/oidcendpoint/oauth2/authorization.py
+++ b/src/oidcendpoint/oauth2/authorization.py
@@ -31,6 +31,7 @@
 from oidcendpoint.exception import ServiceError
 from oidcendpoint.exception import TamperAllert
 from oidcendpoint.exception import ToOld
+from oidcendpoint.exception import UnAuthorizedClientScope
 from oidcendpoint.exception import UnknownClient
 from oidcendpoint.session import setup_session
 from oidcendpoint.user_authn.authn_context import pick_auth
@@ -59,6 +60,21 @@ def re_authenticate(request, authn):
     return False
 
 
+def check_unknown_scopes_policy(request_info, cinfo, endpoint_context):
+    op_capabilities = endpoint_context.conf['capabilities']
+    client_allowed_scopes = cinfo.get('allowed_scopes') or \
+                            op_capabilities['scopes_supported']
+
+    # this prevents that authz would be released for unavailable scopes
+    for scope in request_info['scope']:
+        if op_capabilities.get('deny_unknown_scopes') and \
+           scope not in client_allowed_scopes:
+            _msg = '{} requested an unauthorized scope ({})'
+            logger.warning(_msg.format(cinfo['client_id'],
+                                       scope))
+            raise UnAuthorizedClientScope()
+
+
 class Authorization(Endpoint):
     request_cls = oauth2.AuthorizationRequest
     response_cls = oauth2.AuthorizationResponse
@@ -588,6 +604,11 @@ def process_request(self, request_info=None, **kwargs):
         _cid = request_info["client_id"]
         cinfo = self.endpoint_context.cdb[_cid]
 
+        logger.debug("client {}: {}".format(_cid, cinfo))
+
+        # this apply the default optionally deny_unknown_scopes policy
+        check_unknown_scopes_policy(request_info, cinfo, self.endpoint_context)
+
         cookie = kwargs.get("cookie", "")
         if cookie:
             del kwargs["cookie"]
diff --git a/src/oidcendpoint/oidc/authorization.py b/src/oidcendpoint/oidc/authorization.py
index 7a89963..69141f4 100755
--- a/src/oidcendpoint/oidc/authorization.py
+++ b/src/oidcendpoint/oidc/authorization.py
@@ -34,6 +34,7 @@
 from oidcendpoint.exception import TamperAllert
 from oidcendpoint.exception import ToOld
 from oidcendpoint.exception import UnknownClient
+from oidcendpoint.oauth2.authorization import check_unknown_scopes_policy
 from oidcendpoint.session import setup_session
 from oidcendpoint.user_authn.authn_context import pick_auth
 
@@ -680,6 +681,9 @@ def process_request(self, request_info=None, **kwargs):
         cinfo = self.endpoint_context.cdb[_cid]
         logger.debug("client {}: {}".format(_cid, cinfo))
 
+        # this apply the default optionally deny_unknown_scopes policy
+        check_unknown_scopes_policy(request_info, cinfo, self.endpoint_context)
+
         cookie = kwargs.get("cookie", "")
         if cookie:
             del kwargs["cookie"]
diff --git a/tests/test_24_oauth2_authorization_endpoint.py b/tests/test_24_oauth2_authorization_endpoint.py
index 8c35337..599269d 100755
--- a/tests/test_24_oauth2_authorization_endpoint.py
+++ b/tests/test_24_oauth2_authorization_endpoint.py
@@ -30,6 +30,7 @@
 from oidcendpoint.exception import RedirectURIError
 from oidcendpoint.exception import ToOld
 from oidcendpoint.exception import UnknownClient
+from oidcendpoint.exception import UnAuthorizedClientScope
 from oidcendpoint.exception import UnAuthorizedClient
 from oidcendpoint.id_token import IDToken
 from oidcendpoint.oauth2.authorization import Authorization
@@ -464,6 +465,38 @@ def test_setup_auth_error(self):
 
         item["method"].file = ""
 
+    def test_setup_auth_invalid_scope(self):
+        request = AuthorizationRequest(
+            client_id="client_id",
+            redirect_uri="https://rp.example.com/cb",
+            response_type=["id_token"],
+            state="state",
+            nonce="nonce",
+            scope="openid THAT-BLOODY_SCOPE",
+        )
+        redirect_uri = request["redirect_uri"]
+        cinfo = {
+            "client_id": "client_id",
+            "redirect_uris": [("https://rp.example.com/cb", {})],
+            "id_token_signed_response_alg": "RS256",
+        }
+
+        _ec = self.endpoint.endpoint_context
+        _ec.cdb["client_id"] = cinfo
+
+        kaka = self.endpoint.endpoint_context.cookie_dealer.create_cookie(
+            "value", "sso")
+
+        # force to 400 Http Error message if the release scope policy is heavy!
+        self.endpoint.endpoint_context.conf['capabilities']['deny_unknown_scopes'] = True
+        excp = None
+        try:
+            res = self.endpoint.process_request(request)
+        except UnAuthorizedClientScope as e:
+            excp = e
+        assert excp
+        assert isinstance(excp, UnAuthorizedClientScope)
+
     def test_setup_auth_user(self):
         request = AuthorizationRequest(
             client_id="client_id",