Saving user settings when using federated login
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I need to save settings for each user on my application.

I tried to use the user as a parent of my settings object, but I cannot do this since users do not have keys.
I then created an instance in my settings object that has a reference to user property, but in the docs it says UserProperty is unstable if the user changes their email address.
I then decided to save the user_id in a StringProperty() but if the user logs in with OpenId, the user_id element is None.

Is there a way to tie the user settings to the user object that works for both google accounts and open_id accounts?