in build-android/app/src/main/java/com/google/firebase/codelab/friendlychat/MainActivity.kt [126:135]
public override fun onStart() {
super.onStart()
// Check if user is signed in.
if (auth.currentUser == null) {
// Not signed in, launch the Sign In activity
startActivity(Intent(this, SignInActivity::class.java))
finish()
return
}
}