Flutter OAuth Web View and parse code from Callback in Flutter widget

flutter_webview_oatuh2_screen.dart

// THIS IS JUST AN EXAMPLE AND POSSIBLY ONE SOLUTUON 
import 'dart:async';

import 'package:flutter/material.dart';
import 'package:flutter/widgets.dart';
import 'package:flutter_webview_plugin/flutter_webview_plugin.dart';

class OauthWebCallBackFlutter extends StatefulWidget {
  const OauthWebCallBackFlutter(this.appID);

  final String appID;

  @override
  _OauthWebCallBackFlutterState createState() => _OauthWebCallBackFlutterState();
}

class _OauthWebCallBackFlutterState extends State<OauthWebCallBackFlutter> {
  final FlutterWebviewPlugin flutterWebviewPlugin = FlutterWebviewPlugin();
  StreamSubscription<String> subscription;

  @override
  void initState() {
    subscription = flutterWebviewPlugin.onUrlChanged.listen((String url) {
      const String callbackURL = 'https://example.com/callback';
      if (url.startsWith(callbackURL)) {
        final String code = Uri.parse(url).queryParameters['code'].toString();
        print('CODE $code');
        // DO whatever you want
      }
    });
    super.initState();
  }

  @override
  void dispose() {
    subscription?.cancel();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      backgroundColor: Colors.white,
      appBar: AppBar(),
      body: SafeArea(
        child: WebviewScaffold(
          url:
              'https://somelink/authorize?client_id=secrect&redirect_uri=https://example.com/callback&response_type=code&scope=example',
          clearCookies: true,
          clearCache: true,
          bottomNavigationBar: null,
          geolocationEnabled: false,
          allowFileURLs: false,
          resizeToAvoidBottomInset: true,
          withJavascript: true,
          withLocalStorage: true,
          displayZoomControls: false,
          withZoom: true,
          hidden: true,
        ),
      ),
    );
  }
}