title: Are "Firebase Auth" custom claims eventually consistent?
body: <p>I am using Firebase Auth for SMS login and I want to add to new users a custom "countryCode" claim to the token.
  After the Android app validate the SMS code, it invoke the account service in my backend to create the new account and
  in that step add the custom claim with Firebase Admin SDK.
  The app need to do a force refresh token to get the new claim.</p>
  
  <p>I need to know if after adding the "claim" the update is eventually consistent or not.
  If it is eventually consistent I can't guarantee that the refreshed token have the new claim.</p>