title: Firebase + Flutter : get platform user used to sign in
body: <p>I have an app with 3 sign in methods: Google, Facebook &amp; mail.
  I want to show the users that are signed in with mail a different screen. 
  Is it possible to get the sign in method form the package firebase authentication?</p>
  
  <p>I know I can fix this by using firestore &amp; checking if a statement is true or false. But that will cost me a read every time a user opens the app...</p>