How to determine if a Firebase user is signed in using facebook authentication

For me, the following solution is working. First, get the firebase user object if you have'nt already:

FirebaseAuth mAuth = FirebaseAuth.getInstance();
FirebaseUser firebaseUser = mAuth.getCurrentUser();

Now use the following on the FirebaseUser object to get the sign in provider:

firebaseUser.getIdToken(false).getResult().getSignInProvider()

Sources:

https://firebase.google.com/docs/reference/android/com/google/firebase/auth/FirebaseUser

https://firebase.google.com/docs/reference/android/com/google/firebase/auth/GetTokenResult.html

It will return password, google.com, facebook.com and twitter.com for email, google, facebook and twitter respectively.

In my app, I use Anonymous Firebase accounts. When I connect Firebase auth with a Facebook account or Google Account I am checking like the following:

for (UserInfo user: FirebaseAuth.getInstance().getCurrentUser().getProviderData()) {

  if (user.getProviderId().equals("facebook.com")) { 
    //For linked facebook account
    Log.d("xx_xx_provider_info", "User is signed in with Facebook");

  } else if (user.getProviderId().equals("google.com")) { 
    //For linked Google account
    Log.d("xx_xx_provider_info", "User is signed in with Google");
  }

}

In version 3.x and later a single user can be signed in with multiple providers. So there is no longer the concept of a single provider ID. In fact when you call:

FirebaseAuth.getInstance().getCurrentUser().getProviderId()

It will always return firebase.

To detect if the user was signed in with Facebook, you will have to inspect the provider data:

for (UserInfo user: FirebaseAuth.getInstance().getCurrentUser().getProviderData()) {
  if (user.getProviderId().equals("facebook.com")) {
    System.out.println("User is signed in with Facebook");
  }
}