core: add Serializer for UserSettings, used by stages and sources

Signed-off-by: Jens Langhammer <jens.langhammer@beryju.org>

authentik/flows/models.py

@@ -10,7 +10,7 @@ from model_utils.managers import InheritanceManager
 from rest_framework.serializers import BaseSerializer
 from structlog.stdlib import get_logger
 
-from authentik.flows.challenge import Challenge
+from authentik.core.types import UserSettingSerializer
 from authentik.lib.models import InheritanceForeignKey, SerializerModel
 from authentik.policies.models import PolicyBindingModel
 
@@ -65,7 +65,7 @@ class Stage(SerializerModel):
         raise NotImplementedError
 
     @property
-    def ui_user_settings(self) -> Optional[Challenge]:
+    def ui_user_settings(self) -> Optional[UserSettingSerializer]:
         """Entrypoint to integrate with User settings. Can either return None if no
         user settings are available, or a challenge."""
         return None