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

I am using firebase from google and I have some trouble with user authentication. After logging with facebook I obtain FirebaseUser in AuthStateListener, but how can I detect if this user is logged via facebook or differently?

UPDATE As @Frank van Puffelen said FirebaseAuth.getInstance().getCurrentUser().getProviderId() should return "facebook", but in my case it returns "firebase". Now I cannot figure out what's the reason of this behavior. When I got FacebookToken I do something like this:

        AuthCredential credential = FacebookAuthProvider.getCredential(facebookToken.getToken());
        mAuth.signInWithCredential(credential)
                .addOnCompleteListener(this, new OnCompleteListener<AuthResult>() {
                    @Override
                    public void onComplete(@NonNull Task<AuthResult> task) {

                        // If sign in fails, display a message to the user. If sign in succeeds
                        // the auth state listener will be notified and logic to handle the
                        // signed in user can be handled in the listener.
                        if (!task.isSuccessful()) {

                        }

                    }
                });

And afterthat before onComplete() method is called, my AuthStateListener gets user which provider id is not "facebook" as it should be. Am I doing something wrong? I followed official google documentation

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");
  }
}

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");
  }

}

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.