models_backend: use a dynamic proxy user model

authentic2/backends/models_backend.py

@@ -10,13 +10,27 @@ def upn(username, realm):
     '''Build an UPN from a username and a realm'''
     return u'{0}@{1}'.format(username, realm)
 
+PROXY_USER_MODEL = None
+
+def get_proxy_user_model():
+    global PROXY_USER_MODEL
+    if PROXY_USER_MODEL is None:
+        class ProxyUser(get_user_model()):
+            def roles(self):
+                return self.groups.values_list('name', flat=True)
+
+            class Meta:
+                proxy = True
+        PROXY_USER_MODEL = ProxyUser
+    return PROXY_USER_MODEL
+
 class ModelBackend(ModelBackend):
     """
     Authenticates against settings.AUTH_USER_MODEL.
     """
 
     def get_query(self, username, realm):
-        UserModel = get_user_model()
+        UserModel = get_proxy_user_model()
         username_field = UserModel.USERNAME_FIELD
         queries = []
         try:
@@ -38,10 +52,10 @@ class ModelBackend(ModelBackend):
         return reduce(models.Q.__or__, queries)
 
     def authenticate(self, username=None, password=None, realm=None, **kwargs):
-        UserModel = get_user_model()
+        UserModel = get_proxy_user_model()
         if username is None:
             username = kwargs.get(UserModel.USERNAME_FIELD)
         query = self.get_query(username, realm)
-        for user in UserModel._default_manager.filter(query):
+        for user in UserModel.objects.filter(query):
             if user.check_password(password):
                 return user