App Engine callback for new user "registration" / user login?
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I'm using Google App Engine's default User service for authentication right now.  I would like to be able to store the join date for a user (i.e. how long the user has been a member of my web app) and be able to ban users from my app if they misbehave.

I understand that I will need an additional model to store this information:

    class User_Info(db.model):
      user = db.UserProperty()
      join_date = db.DateTimeProperty(auto_now_add=True)
      banned = db.BooleanProperty(False)

But what I don't understand: is there a way is to get a callback for when a new user "registers" for my app (to store the join date) or logs in (to check if user has been banned)?

One method I thought of was to send in a intermediary destination URL to the `users.create_login_url()`, which would check if an associated User_Info instance existed.  If it did, it would check the banned flag.  If not, it would create a user_info instance and store the join date.  It would then redirect to the actual destination url.

Is there a better solution? 

Note that I will switch over to the federated authentication model in the future and was hoping for a solution that would work when I did switch over.

Thanks!