FirebaseAuth_onCreate

override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_login)

        // initialise the FirebaseAuth instance
        mAuth = FirebaseAuth.getInstance()

        // Configure Google Sign In
        mGoogleSignInOptions = GoogleSignInOptions.Builder(GoogleSignInOptions.DEFAULT_SIGN_IN)
                .requestIdToken(getString(R.string.default_web_client_id))
                .requestEmail()
                .build()

        // configure the GoogleApiClient
        mGoogleApiClient = GoogleApiClient
                .Builder(this)
                .enableAutoManage(this  , this).addApi(Auth.GOOGLE_SIGN_IN_API , mGoogleSignInOptions).build()



        button_login.setOnClickListener {
            if(isUserLoggedIn){
                doLogout()
            }else{
                doLogin()
            }
        }
    }