feat: add example

Signed-off-by: The one with the braid <[email protected]>

Author: TheOneWithTheBraid

lib/msc_extensions/msc_3861_native_oidc/README.md

@@ -0,0 +1,56 @@
+# Implement \[matrix\] OIDC using the Matrix Dart SDK
+
+```dart
+import 'dart:async';
+
+import 'package:flutter/foundation.dart';
+
+import 'package:matrix/matrix.dart';
+import 'package:url_launcher:url_launcher.dart';
+
+Future<void> main() async {
+  final client = Client(
+    // [...]
+  );
+
+  await client.checkHomeserver(myHomeserver);
+
+  final name = 'My [matrix] client on web';
+
+  final registrationData = OidcDynamicRegistrationData.localized(
+    contacts: {myOidcAdminContact},
+    url: 'https://example.com',
+    defaultLocale: myDefaultLocale,
+    localizations: {
+      'fr_FR': LocalizedOidcClientMetadata(
+        // [...]
+      )
+    },
+    redirect: kIsWeb
+        ? { 'http://localhost:0'}
+        : {
+      Uri.parse('com.example:/oauth2redirect/'),
+      Uri.parse('http://localhost/oauth2redirect/'),
+    },
+    applicationType: kIsWeb ? 'web' : 'native',
+  );
+
+  final oidcClientId = await client.oidcEnsureDynamicClientId(
+    registrationData,
+  );
+
+  // You can e.g. use `package:app_links` to forward the called deep link into this completer
+  final nativeCompleter = Completer<OidcCallbackResponse>();
+
+  await client.oidcAuthorizationGrantFlow(
+    nativeCompleter: nativeCompleter,
+    oidcClientId: oidcClientId,
+    redirectUri: client.oAuth2RedirectUri,
+    launchOAuth2Uri: launchUrl,
+    responseMode: kIsWeb ? 'fragment' : 'query',
+    prompt: 'consent',
+    initialDeviceDisplayName: name,
+    enforceNewDeviceId: true,
+  );
+}
+```