oauth2_sign_in_using_auth_service.dart

Future validateEmailWithOAuth2AndLogin(LoginMethod loginMethod) async {
  // Creates an empty email validation token on server-side so we have its ID
  EmailValidationToken emailValidationToken = await beginOAuth2EmailValidation(loginMethod);

  String url = 'https://auth.youapp.com/?${kIsWeb ? 'platform=web&' : ''}provider=${loginMethod.name}&token=${emailValidationToken.id}';

  if (await canLaunchUrlString(url)) {
    // Open the URL in a new browser window on all the platforms except web
    await launchUrlString(
      url,
      mode: kIsWeb ? LaunchMode.platformDefault : LaunchMode.externalApplication,
      webOnlyWindowName: '_self',
    );
  }

  // On web user leaves the app while signing in, so we do not need to check the email validation token state
  if (kIsWeb) return;

  DateTime start = DateTime.now();

  _timer = Timer.periodic(
    const Duration(seconds: 3),
    (timer) async {
      if ((await endOAuth2EmailValidation(loginMethod, emailValidationToken.id!))?.email?.isNotEmpty == true) {
        _timer?.cancel();
        await loginWithValidatedEmail(emailValidationToken);
      }
    },
  );
}