flows: handle missing `initial_data` in challenge

AUTHENTIK-1HK

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

authentik/flows/stage.py

@@ -138,6 +138,8 @@ class ChallengeStageView(StageView):
             op="authentik.flow.stage._get_challenge",
             description=self.__class__.__name__,
         ):
+            if not hasattr(challenge, "initial_data"):
+                challenge.initial_data = {}
             if "flow_info" not in challenge.initial_data:
                 flow_info = ContextualFlowInfo(
                     data={