Android Studio – Get Firebase token from GetIdToken

I have done the following in Swift:

let currentUser = Auth.auth().currentUser
currentUser?.getTokenForcingRefresh(true) {idToken, error in
   if let error = error {
     // Handle error
     print("error (below)")
     print(error)
     return;
   }
   print("idToken = " + idToken!) // token looks like this: kpJhbGRiOiJSUzI1NiIsIntpZCI9Ijg0MjIuYzc3NTWkOWZmTjI3OBQxZTkyNTpkNWZjZjUwNzg2YTFmNGIifQ.eyJpc3MiOiJodHRwczovL3NlY3Vy... (it's really long)
   //..do stuff with token
}

I am now trying to do the equivalent for Android. The firebase documentation touches on the topic but does not explain getting the token extensively. I have tried the following:

Log.d(TAG, user.getIdToken(true));

However, this gives me the following error when I attempt to authenticate this alone on my backend server:

Error: Decoding Firebase ID token failed. Make sure you passed the
entire string JWT which represents an ID token. See
https://firebase.google.com/docs/auth/admin/verify-id-tokens for
details on how to retrieve an ID token.
at FirebaseAuthError.Error (native)
at FirebaseAuthError.FirebaseError [as constructor] (/user_code/node_modules/firebase-admin/lib/utils/error.js:25:28)
at new FirebaseAuthError (/user_code/node_modules/firebase-admin/lib/utils/error.js:90:23)
at FirebaseTokenGenerator.verifyIdToken (/user_code/node_modules/firebase-admin/lib/auth/token-generator.js:155:35)
at Auth.verifyIdToken (/user_code/node_modules/firebase-admin/lib/auth/auth.js:104:37)
at admin.database.ref.child.child.child.child.child.child.orderByChild.once.then.snapshot
(/user_code/index.js:1430:22)
at process._tickDomainCallback (internal/process/next_tick.js:135:7)

I believe this is because there needs to be an onSuccessListener but am not sure, nor have had success implementing it as follows:

user.getIdToken(true).addOnSuccessListener(new OnSuccessListener<UploadTask.TaskSnapshot>() {
  @Override
  public void onSuccess(UploadTask.TaskSnapshot taskSnapshot) {
    Log.d(TAG, "onSuccess: taskSnapshot = " + taskSnapshot);
  }
});

Your second approach is close, you just need to use OnSuccessListener<GetTokenResult> instead of <UploadTask.TaskSnapshot> as that is for uploading images with Firebase Storage.

Try this:

user.getIdToken(true).addOnSuccessListener(new OnSuccessListener<GetTokenResult>() {
  @Override
  public void onSuccess(GetTokenResult result) {
    String idToken = result.getToken();
    //Do whatever
    Log.d(TAG, "GetTokenResult result = " + idToken);
  }
}