Getting Firebase user token synchronously

Question

I am trying to get a Firebase token to authenticate my calls to a Rest API. I can generate the tokens asynchronously with the following code.

    FirebaseUser mUser = App.getFirebaseAuth().getCurrentUser();
    if (mUser!=null) {
        mUser.getIdToken(false)
                .addOnCompleteListener(new OnCompleteListener<GetTokenResult>() {
                    public void onComplete(@NonNull Task<GetTokenResult> task) {
                        if (task.isSuccessful()) {
                            ID_TOKEN = task.getResult().getToken();
                        } else {
                            Log.e(App.TAG, "Firebase Token task ended with error.");
                        }
                    }
                });
    } else {
        Log.i(App.TAG,"User is null, no Firebase Token available");
    }

The ID_TOKEN is a static string variable that holds the result. The issue is, I am constructing my request and adding the authentication headers.

        headers.put("Authentication",
                "Bearer  + ID_TOKEN);

The issue is, since the Firebase token is retrieved asynchronously, sometims the ID_TOKEN variable is empty. I tried forcing the thread to wait for the task using

Tasks.await(task)

But I get an exception saying await cannot be invoked in the main thread.

Is there any other way to get the token synchronously, or make the thread wait until the tasks finishes?

Answer 1

I'm doing it like this now:

private suspend fun getTokenResult (firebaseUser: FirebaseUser) = suspendCoroutine<GetTokenResult?> { continuation ->
firebaseUser.getIdToken(true).addOnCompleteListener {
    if (it.isSuccessful) {
        continuation.resume(it.result)
    } else {
        continuation.resume(null)
    }
}

Using a suspended function and the continuation mechanism. So if you are using Coroutines, this might be the easiest way

Answer 2

I had the same problem, I needed to update token in Retrofit Authenticator when I got 407. I use CountDownLatch

override fun authenticate(route: Route?, response: Response): Request? {
    val user = FirebaseAuth.getInstance().currentUser
    var token: String? = null
    val lock = CountDownLatch(1)

    user?.getIdToken(true)?.addOnCompleteListener { task ->
        if (task.isSuccessful) {
            token = task.result?.token
            if (token == null) {
                lock.countDown()            //<--unlock 
                return@addOnCompleteListener
            }
            //save token
        } else {
            lock.countDown()                //<--unlock 
            return@addOnCompleteListener
        }
    }
    lock.await()                            //<--wait unlock 

    return if (token != null)
        response.request().newBuilder().header(AUTHORIZATION_KEY, token).build()
    else null
}