Google Sign In implemented in Kotlin

MainActivity.kt

class MainActivity : AppCompatActivity(), GoogleApiClient.OnConnectionFailedListener {
    private val RC_SIGN_IN = 9001

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        val binding : MainActivityBinding = DataBindingUtil.setContentView(this, R.layout.activity_main)

        val googleSignInOptions : GoogleSignInOptions = GoogleSignInOptions
                .Builder(GoogleSignInOptions.DEFAULT_SIGN_IN)
                .requestEmail()
                .build()

        val googleApiClient = GoogleApiClient
                .Builder(this)
                .enableAutoManage(this, this)
                .addApi(Auth.GOOGLE_SIGN_IN_API, googleSignInOptions)
                .build()

        binding.signInButton.setOnClickListener({
            val intent : Intent = Auth.GoogleSignInApi.getSignInIntent(googleApiClient)
            startActivityForResult(intent, RC_SIGN_IN)
        })
    }

    override fun onConnectionFailed(p0: ConnectionResult) {

    }

    override fun onActivityResult(requestCode: Int, resultCode: Int, data: Intent?) {
        super.onActivityResult(requestCode, resultCode, data)

        if(requestCode == RC_SIGN_IN) {
            val result : GoogleSignInResult = Auth.GoogleSignInApi.getSignInResultFromIntent(data)
            handleSignInResult(result)
        }
    }

    private fun handleSignInResult(signInResult: GoogleSignInResult) {
        if(signInResult.isSuccess) {
            // Authenticated
            val account : GoogleSignInAccount? = signInResult.signInAccount
        } else {
            // Failed
        }
    }
}