Add appCheck registration

Author: cynthiajoan

packages/firebase_ai/firebase_ai/lib/src/firebase_ai.dart

@@ -68,6 +68,7 @@ class FirebaseAI extends FirebasePluginPlatform {
     bool? useLimitedUseAppCheckTokens,
   }) {
     app ??= Firebase.app();
+    appCheck ??= app.getService<FirebaseAppCheck>();
     var instanceKey = '${app.name}::vertexai::$location';
 
     if (_cachedInstances.containsKey(instanceKey)) {
@@ -100,6 +101,7 @@ class FirebaseAI extends FirebasePluginPlatform {
     bool? useLimitedUseAppCheckTokens,
   }) {
     app ??= Firebase.app();
+    appCheck ??= app.getService<FirebaseAppCheck>();
     var instanceKey = '${app.name}::googleai';
 
     if (_cachedInstances.containsKey(instanceKey)) {

packages/firebase_ai/firebase_ai/test/firebase_vertexai_test.dart

@@ -96,6 +96,13 @@ void main() {
       expect(vertexAIAppCheck.useLimitedUseAppCheckTokens, true);
     });
 
+    test('Instance creation with auto-injected AppCheck', () {
+      final vertexAI = FirebaseAI.vertexAI(app: customApp);
+      
+      expect(vertexAI.app, equals(customApp));
+      expect(vertexAI.appCheck, equals(customAppCheck));
+    });
+
     test('generativeModel creation with Grounding tools', () {
       final ai = FirebaseAI.googleAI();
 

packages/firebase_app_check/firebase_app_check/lib/src/firebase_app_check.dart

@@ -41,7 +41,9 @@ class FirebaseAppCheck extends FirebasePluginPlatform {
   /// Returns an instance using a specified [FirebaseApp].
   static FirebaseAppCheck instanceFor({required FirebaseApp app}) {
     return _firebaseAppCheckInstances.putIfAbsent(app.name, () {
-      return FirebaseAppCheck._(app: app);
+      final instance = FirebaseAppCheck._(app: app);
+      app.registerService<FirebaseAppCheck>(instance);
+      return instance;
     });
   }
 

packages/firebase_core/firebase_core/lib/src/firebase_app.dart

@@ -71,4 +71,21 @@ class FirebaseApp {
 
   @override
   String toString() => '$FirebaseApp($name)';
+
+  static final Map<String, Map<Type, dynamic>> _registries = {};
+
+  /// Registers a service instance for this app.
+  void registerService<T>(T service) {
+    final registry = _registries.putIfAbsent(name, () => {});
+    registry[T] = service;
+  }
+
+  /// Returns a registered service instance for this app.
+  T? getService<T>() {
+    final registry = _registries[name];
+    if (registry != null) {
+      return registry[T] as T?;
+    }
+    return null;
+  }
 }

packages/firebase_core/firebase_core/test/firebase_core_test.dart

@@ -64,6 +64,16 @@ void main() {
         mock.app(testAppName),
       ]);
     });
+
+    test('.registerService() and .getService()', () {
+      FirebaseApp app = Firebase.app(testAppName);
+      
+      const testService = 'testServiceInstance';
+      app.registerService<String>(testService);
+      
+      expect(app.getService<String>(), testService);
+      expect(app.getService<int>(), isNull);
+    });
   });
 
   test('.initializeApp() with demoProjectId', () async {