Flutter Firebase Phone Authentication

image source https://www.youtube.com/watch?v=uaerc_uy-ME&ab_channel=SantosEnoque
Flutter supports varius ways to log in to firebase authentication.
One of them is the phone verification, which google sends OTP to the user's phone number.
This sign in function requires PhoneAuthCredential

FirebaseAuth _auth = FirebaseAuth.instance;

  String verificationId = '';
  bool showLoading = false;

  void signInWithPhoneAuthCredential(
      PhoneAuthCredential phoneAuthCredential) async {
    setState(() {
      showLoading = true;
    });

    try {
      final authCredential =
          await _auth.signInWithCredential(phoneAuthCredential);
      setState(() {
        showLoading = false;
      });
      if (authCredential.user != null) {
        Navigator.pushReplacement(
            context, MaterialPageRoute(builder: (context) => LandingRoute()));
      }
    } on Exception catch (e) {
      setState(() {
        showLoading = false;
        print('err from signInWithPhoneAUthCredential function call back');
        currentState = MobileVerificationState.SHOW_MOBILE_FORM_STATE;
      });
      print(e);
    }
  }

PhoneAuthCredential is created via

await _auth.verifyPhoneNumber(
                    phoneNumber: processedPhoneNumber,
                    verificationCompleted: (phoneAuthCredential) async {
                      setState(() {
                        print('verificationCompleted');
                        showLoading = false;
                      });
                      signInWithPhoneAuthCredential(
                          phoneAuthCredential); //not needed yet
                    },
                    verificationFailed: (verificationFailed) async {
                      setState(() {
                        print('verificationFailed');
                        showLoading = false;
                      });

                      print(verificationFailed.message);
                      setState(() {
                        showLoading = false;
                        currentState =
                            MobileVerificationState.SHOW_MOBILE_FORM_STATE;
                      });
                      print('error from verificationFailed');
                    },
                    codeSent: (verificationId, resendingToken) async {
                      print('codeSent');
                      setState(() {
                        showLoading = false;
                        currentState =
                            MobileVerificationState.SHOW_OPT_FORM_STATE;
                        this.verificationId = verificationId;
                      });
                    },
                    codeAutoRetrievalTimeout: (verificationId) async {},
                  );
                }

ライターと火線ライターで携帯電話にログインすることができます.
なお、Admin SDKを使用しないと、会員加入の有無を事前にチェックすることはできません.
このメソッドは、電子メールでログインしたときにauthになりました.内蔵されていますが、phoneAuthの場合はそうではありません.
このためfirstoreにユーザー情報を入力してログイン時にサーバをロードしようとしますが、セキュリティルール上auth変数なしでサーバにアクセスするべきではありません.
Firebasecloud functionで他のバックエンドサーバなしで行えるようですが、さらに勉強が必要です.