title: How to wait for FirebaseAuth to finish initializing?
body: <p>Integrated Firebase Authentication to my app. Everything seems to be fine, until I noticed the issue wherein I open the app, it shows me the login screen, even though there is already a user signed in. </p>
  
  <p>Exiting the app and launching it again solves the problem (app no longer asks the user to sign in again), though it provides the users a very bad experience.</p>
  
  <p>I've read the docs, and apparently, calling <code>FirebaseAuth.getInstance().getCurrentUser()</code> might return null if auth haven't finished initializing. I'm assuming that's the reason why the issue happens. So I wonder if there is a way to wait for FirebaseAuth to finish its initialization before I can call getCurrentUser()?</p>