Fix issue #636, pass request object to authenticate function. (#643)

Author: W0126

oauth2_provider/oauth2_validators.py

@@ -611,7 +611,7 @@ def validate_user(self, username, password, client, request, *args, **kwargs):
         """
         Check username and password correspond to a valid and active User
         """
-        u = authenticate(username=username, password=password)
+        u = authenticate(request, username=username, password=password)
         if u is not None and u.is_active:
             request.user = u
             return True