[flutter_appauth] Add custom browser with user cancellation handling

flutter_appauth/example/lib/main.dart

@@ -16,8 +16,9 @@
   State<MyApp> createState() => _MyAppState();
 }
 
-class _MyAppState extends State<MyApp> {
+class _MyAppState extends State<MyApp> with WidgetsBindingObserver {
   bool _isBusy = false;
+  bool _isAuthFlowInProgress = false;
   final FlutterAppAuth _appAuth = const FlutterAppAuth();
 
   String? _codeVerifier;
@@ -62,6 +63,30 @@
     endSessionEndpoint: 'https://demo.duendesoftware.com/connect/endsession',
   );
 
+  @override
+  void initState() {
+    super.initState();
+    WidgetsBinding.instance.addObserver(this);
+  }
+
+  @override
+  void dispose() {
+    WidgetsBinding.instance.removeObserver(this);
+    super.dispose();
+  }
+
+  @override
+  void didChangeAppLifecycleState(AppLifecycleState state) {
+    if (state == AppLifecycleState.resumed) {
+      if (_isAuthFlowInProgress) {
+        setState(() {
+          _isAuthFlowInProgress = false;
+          _clearBusyState();
+        });
+      }
+    }
+  }
+
   @override
   Widget build(BuildContext context) {
     return MaterialApp(
@@ -126,6 +151,19 @@
                               ExternalUserAgent.sfSafariViewController),
                     ),
                   ),
+                if (Platform.isIOS)
+                  Padding(
+                    padding: const EdgeInsets.all(8.0),
+                    child: ElevatedButton(
+                      child: const Text(
+                        'Auto code exchange using system browser (iOS only)',
+                        textAlign: TextAlign.center,
+                      ),
+                      onPressed: () => _signInWithAutoCodeExchange(
+                        externalUserAgent:
+                          ExternalUserAgent.customBrowser),
+                    ),
+                  ),
                 ElevatedButton(
                   onPressed: _refreshToken != null ? _refresh : null,
                   child: const Text('Refresh token'),
@@ -335,21 +373,28 @@
       {ExternalUserAgent externalUserAgent =
           ExternalUserAgent.asWebAuthenticationSession}) async {
     try {
-      _setBusyState();
+      _setBusyState(isAuthFlow: externalUserAgent == ExternalUserAgent.customBrowser);
 
       /*
         This shows that we can also explicitly specify the endpoints rather than
         getting from the details from the discovery document.
       */
-      final AuthorizationTokenResponse result =
-          await _appAuth.authorizeAndExchangeCode(
+      final Future<AuthorizationTokenResponse> authRequest =
+      _appAuth.authorizeAndExchangeCode(
         AuthorizationTokenRequest(_clientId, _redirectUrl,
             serviceConfiguration: _serviceConfiguration,
             scopes: _scopes,
             externalUserAgent: externalUserAgent),
       );
 
-      /* 
+      // Apply timeout only when using an external browser user agent.
+      final AuthorizationTokenResponse result =
+      externalUserAgent == ExternalUserAgent.customBrowser
+          ? await authRequest.timeout(const Duration(minutes: 2))
+          : await authRequest;
+
+
+      /*
         This code block demonstrates passing in values for the prompt
         parameter. In this case it prompts the user login even if they have
         already signed in. the list of supported values depends on the
@@ -402,10 +447,13 @@
     });
   }
 
-  void _setBusyState() {
+  void _setBusyState({bool? isAuthFlow = null}) {
     setState(() {
       _error = '';
       _isBusy = true;
+      if (isAuthFlow != null) {
+        _isAuthFlowInProgress = isAuthFlow;
+      }
     });
   }
 

flutter_appauth/ios/flutter_appauth/Sources/flutter_appauth/AppAuthIOSAuthorization.m

@@ -173,6 +173,9 @@ @implementation AppAuthIOSAuthorization
     return [[OIDExternalUserAgentIOSSafariViewController alloc]
         initWithPresentingViewController:rootViewController];
   }
+  if ([externalUserAgent integerValue] == CustomBrowser) {
+    return [OIDExternalUserAgentIOSCustomBrowser CustomBrowserSafari];
+  }
   return [[OIDExternalUserAgentIOS alloc]
       initWithPresentingViewController:rootViewController];
 }

flutter_appauth/ios/flutter_appauth/Sources/flutter_appauth/FlutterAppAuth.h

@@ -61,7 +61,8 @@ static NSString *const END_SESSION_ERROR_MESSAGE_FORMAT =
 typedef NS_ENUM(NSInteger, ExternalUserAgent) {
   ASWebAuthenticationSession,
   EphemeralASWebAuthenticationSession,
-  SafariViewController
+  SafariViewController,
+  CustomBrowser
 };
 
 @interface AppAuthAuthorization : NSObject

flutter_appauth_platform_interface/lib/src/external_user_agent.dart

@@ -45,5 +45,12 @@ enum ExternalUserAgent {
   /// Note that as this does not follow the best practices on using the
   /// appropriate native APIs based on the OS version, developers should use
   /// this at their own discretion.
-  sfSafariViewController
+  sfSafariViewController,
+
+
+  /// Indicates a preference for using an external user-agent,
+  /// suitable for e.g. the secure browser of a MDM solution,
+  /// SSO flows and using the cookies/context of the system main browser.
+  /// This is only applicable to iOS (fallback is [asWebAuthenticationSession]).
+  customBrowser
 }