How to get Access Token after authenticating from google firebase in Xamarin android app in c#?

Question

I am working in Xamarin android app in c# with google firebase authentication. The code is working fine with firebase. it is authenticating the user while login and returning the name and email address. But I need the access token after authentication in firebase , to work further with REST API. but I am unable to get the access token , can I get the access token?

Code is as follows:

using Android.App;
using Android.OS;
using Android.Support.V7.App;
using Android.Runtime;
using Android.Widget;
using Android.Gms.Auth.Api.SignIn;
using Android.Gms.Common.Apis;
using Android.Gms.Auth.Api;
using Firebase.Auth;
using Firebase;
using Android.Content;
using System;
using Android.Gms.Tasks;
using Java.Lang;


namespace loginGoogle
{
    [Activity(Label = "@string/app_name", Theme = "@style/AppTheme", MainLauncher = true)]
    public class MainActivity : AppCompatActivity, IOnSuccessListener, IOnFailureListener, IOnCompleteListener
    {
        GoogleSignInOptions gso;
        GoogleApiClient googleApiClient;

        FirebaseAuth firebaseAuth;
        Button signinButton;
        protected override void OnCreate(Bundle savedInstanceState)
        {
            base.OnCreate(savedInstanceState);

            // Set our view from the "main" layout resource
            SetContentView(Resource.Layout.activity_main);

            signinButton = (Button)FindViewById(Resource.Id.signInButton);

            signinButton.Click += SigninButton_Click;

            gso = new GoogleSignInOptions.Builder(GoogleSignInOptions.DefaultSignIn)
                .RequestIdToken("759281956917-ib3rko81uvs4bvdf3g3p76f0dl7q8k64.apps.googleusercontent.com")
                .RequestEmail()
                .Build();

            googleApiClient = new GoogleApiClient.Builder(this)
                .AddApi(Auth.GOOGLE_SIGN_IN_API, gso).Build();
            googleApiClient.Connect();

            firebaseAuth = GetFirebaseAuth();
            UpdateUI();
        }


        private FirebaseAuth GetFirebaseAuth()
        {
            var app = FirebaseApp.InitializeApp(this);
            FirebaseAuth mAuth;

            if (app == null)
            {
                var options = new FirebaseOptions.Builder()
                    .SetProjectId("login-bde5d")
                    .SetApplicationId("login-bde5d")
                    .SetApiKey("AIzaSyCql6njOSplLxy6Nd2tpNHNSeBxyOm6TQM")
                    .SetDatabaseUrl("https://login-bde5d.firebaseio.com")
                    .SetStorageBucket("login-bde5d.appspot.com")
                    .Build();

                app = FirebaseApp.InitializeApp(this, options);
                mAuth = FirebaseAuth.Instance;

            }
            else
            {
                mAuth = FirebaseAuth.Instance;
            }
            return mAuth;
        }
        private void SigninButton_Click(object sender, System.EventArgs e)
        {
            UpdateUI();
            if (firebaseAuth.CurrentUser == null)
            {
                var intent = Auth.GoogleSignInApi.GetSignInIntent(googleApiClient);
                StartActivityForResult(intent, 1);
            }
            else
            {
                firebaseAuth.SignOut();
                UpdateUI();
            }
        }

        protected override void OnActivityResult(int requestCode, [GeneratedEnum] Result resultCode, Intent data)
        {
            base.OnActivityResult(requestCode, resultCode, data);

            if (requestCode == 1)
            {
                GoogleSignInResult result = Auth.GoogleSignInApi.GetSignInResultFromIntent(data);
                if (result.IsSuccess)
                {
                    GoogleSignInAccount account = result.SignInAccount;
                    LoginWithFirebase(account);
                }
            }
        }

        private void LoginWithFirebase(GoogleSignInAccount account)
        {
            var credentials = GoogleAuthProvider.GetCredential(account.IdToken, null);
            firebaseAuth.SignInWithCredential(credentials).AddOnSuccessListener(this)
                .AddOnFailureListener(this).AddOnCompleteListener(this, this);
        }

        public void OnSuccess(Java.Lang.Object result)
        {            
            TextView displayNameText = (TextView)FindViewById(Resource.Id.displaynameText);
            TextView emailText = (TextView)FindViewById(Resource.Id.emailText);

            displayNameText.Text = "Display Name: " + firebaseAuth.CurrentUser.DisplayName;
            emailText.Text = "Email: " + firebaseAuth.CurrentUser.Email;            

            Toast.MakeText(this, "Login successful", ToastLength.Short).Show();
            UpdateUI();
        }

        public void OnFailure(Java.Lang.Exception e)
        {
            Toast.MakeText(this, "Login Failed", ToastLength.Short).Show();
            UpdateUI();
        }
        void UpdateUI()
        {
            if (firebaseAuth.CurrentUser != null)
            {
                signinButton.Text = "Sign Out";
            }
            else
            {
                signinButton.Text = "Sign In With Google";
            }
        }

        public void OnComplete(Task task)
        {
            //throw new NotImplementedException();
            if (task.IsSuccessful)
            {                
                TextView photourlText = (TextView)FindViewById(Resource.Id.photoURLText);
                photourlText.Text = "User successfully login with Photo URL: " + firebaseAuth.CurrentUser.PhotoUrl.Path;

            }
            else
            {
                TextView photourlText = (TextView)FindViewById(Resource.Id.photoURLText);
                photourlText.Text = "problem in user login";
            }
        }
    }
}

I have followed the following link: https://www.youtube.com/watch?v=NYMCrD9klA0

Answer 1

The other answer is referring to a token which is used for Firebase Cloud Messaging / Push notifications not the token which is used for Firebase Auth which is what OP needs.

Once you have logged the user in, this populates FirebaseAuth.Instance.CurrentUser. You can then get the token from the logged in user.

if (FirebaseAuth.Instance.CurrentUser != null)
{
    var tokenRequest = await FirebaseAuth.Instance.CurrentUser.GetIdTokenAsync(true);
    string token = tokenRequest.Token;

    // Do whatever with token
}

Note. There appears to be a bug with current Xamarin Firebase Auth which causes a null reference exception to be raised when calling the GetIdTokenAsync() method on a FirebaseUser object.

'Attempt to invoke virtual method 'com.google.android.gms.tasks.Task com.google.firebase.auth.FirebaseAuth.zza(com.google.firebase.auth.FirebaseUser, boolean)' on a null object reference'

The resolution is documented here - https://github.com/xamarin/GooglePlayServicesComponents/issues/223

Which is to install an additional Nuget package - https://www.nuget.org/packages/Xamarin.Android.ManifestMerger/1.0.0-preview03

Answer 2

You could use the code below to get the token. It would output in output window, or you could get it directly from the code: FirebaseInstanceId.Instance.Token.

Log.Debug(TAG, "InstanceID token: " + FirebaseInstanceId.Instance.Token)

You could refer to the MS docs about Remote Notifications with Firebase Cloud Messaging. https://learn.microsoft.com/en-us/xamarin/android/data-cloud/google-messaging/remote-notifications-with-fcm?tabs=windows

And download the source file from the link below. https://learn.microsoft.com/zh-cn/samples/xamarin/monodroid-samples/firebase-fcmnotifications/