User Authentication (Google) Sign in to the application with Google

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Note: If you experience issues with Google Auth, revisit the Firebase Setup section to ensure the SHA fingerprint has been setup on your local machine.

Auth Service

Create an auth service to isolate the business logic for Firebase authentication methods and user management.

file_type_dartlang auth.dart 
import 'package:firebase_auth/firebase_auth.dart';
import 'package:google_sign_in/google_sign_in.dart';
import 'package:cloud_firestore/cloud_firestore.dart';
import 'dart:async';

class AuthService {
  final GoogleSignIn _googleSignIn = GoogleSignIn();
  final FirebaseAuth _auth = FirebaseAuth.instance;
  final Firestore _db = Firestore.instance;

  // Firebase user one-time fetch
  Future<FirebaseUser> get getUser => _auth.currentUser();

  // Firebase user a realtime stream
  Stream<FirebaseUser> get user => _auth.onAuthStateChanged;

  /// Sign in with Google
  Future<FirebaseUser> googleSignIn() async {
    try {
      GoogleSignInAccount googleSignInAccount = await _googleSignIn.signIn();
      GoogleSignInAuthentication googleAuth =
          await googleSignInAccount.authentication;

      final AuthCredential credential = GoogleAuthProvider.getCredential(
        accessToken: googleAuth.accessToken,
        idToken: googleAuth.idToken,
      );

      AuthResult result = await _auth.signInWithCredential(credential);
      FirebaseUser user = result.user;

      // Update user data
      updateUserData(user);

      return user;
    } catch (error) {
      print(error);
      return null;
    }
  }

  /// Anonymous Firebase login
  Future<FirebaseUser> anonLogin() async {
    AuthResult result = await _auth.signInAnonymously();
    FirebaseUser user = result.user;

    updateUserData(user);
    return user;
  }

  /// Updates the User's data in Firestore on each new login
  Future<void> updateUserData(FirebaseUser user) {
    DocumentReference reportRef = _db.collection('reports').document(user.uid);

    return reportRef.setData({'uid': user.uid, 'lastActivity': DateTime.now()},
        merge: true);
  }

  // Sign out
  Future<void> signOut() {
    return _auth.signOut();
  }
}

Current User with Provider

Access the current user with Provider.

file_type_dartlang main.dart 
import 'package:firebase_auth/firebase_auth.dart';

Widget build(BuildContext context) {
    return MultiProvider(
      providers: [
        StreamProvider<FirebaseUser>.value(value: AuthService().user)
      ],
      child: MaterialApp(
          // omitted
      )
}

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