otp verification in flutter without firebase code example

Example: sigup and sign out using firebase auth in flutter

Future<Null> _signOut() async {
    await _auth.signOut();
    this.setState(() {
      isLoading = false;
    });
    Navigator.of(context).pushAndRemoveUntil(
        MaterialPageRoute(builder: (context) => MyApp()),
        (Route<dynamic> route) => false);
  }