flutter_web_auth.dart

import 'dart:async';
import 'dart:core';

import 'package:flutter/cupertino.dart';
import 'package:flutter/services.dart' show MethodChannel;

class _OnAppLifecycleResumeObserver extends WidgetsBindingObserver {
  final Function onResumed;

  _OnAppLifecycleResumeObserver(this.onResumed);

  @override
  void didChangeAppLifecycleState(AppLifecycleState state) {
    if (state == AppLifecycleState.resumed) {
      onResumed();
    }
  }
}

class FlutterWebAuth {
  static const MethodChannel _channel = const MethodChannel('flutter_web_auth');
  static RegExp _schemeRegExp = new RegExp(r"^[a-z][a-z0-9+.-]*$");

  static final _OnAppLifecycleResumeObserver _resumedObserver = _OnAppLifecycleResumeObserver(() {
    _cleanUpDanglingCalls(); // unawaited
  });

  /// Ask the user to authenticate to the specified web service.
  ///
  /// The page pointed to by [url] will be loaded and displayed to the user. From the page, the user can authenticate herself and grant access to the app. On completion, the service will send a callback URL with an authentication token, and this URL will be result of the returned [Future].
  ///
  /// [callbackUrlScheme] should be a string specifying the scheme of the url that the page will redirect to upon successful authentication.
  /// [preferEphemeral] if this is specified as `true`, an ephemeral web browser session will be used where possible (`FLAG_ACTIVITY_NO_HISTORY` on Android, `prefersEphemeralWebBrowserSession` on iOS/macOS)
  ///
  /// [debug] flag - used for avoid comparing Url.base.origin and messageEvent.origin that gives us opportunity to test without deploy (ex. deployed back example.com and local flutter app localhost)
  static Future<String> authenticate({required String url, required String callbackUrlScheme, bool? preferEphemeral, bool? debug}) async {
    if (!_schemeRegExp.hasMatch(callbackUrlScheme)) {
      throw ArgumentError.value(callbackUrlScheme, 'callbackUrlScheme', 'must be a valid URL scheme');
    }

    WidgetsBinding.instance.removeObserver(_resumedObserver); // safety measure so we never add this observer twice
    WidgetsBinding.instance.addObserver(_resumedObserver);
    return await _channel.invokeMethod('authenticate', <String, dynamic>{
      'url': url,
      'debug': debug ?? false,
      'callbackUrlScheme': callbackUrlScheme,
      'preferEphemeral': preferEphemeral ?? false,
    }) as String;
  }

  /// On Android, the plugin has to store the Result callbacks in order to pass the result back to the caller of
  /// `authenticate`. But if that result never comes the callback will dangle around forever. This can be called to
  /// terminate all `authenticate` calls with an error.
  static Future<void> _cleanUpDanglingCalls() async {
    await _channel.invokeMethod('cleanUpDanglingCalls');
    WidgetsBinding.instance.removeObserver(_resumedObserver);
  }
}