feat(appcheck): Implement reCAPTCHA Enterprise App Check provider

appcheck/firebase-appcheck-recaptchaenterprise/src/main/java/com/google/firebase/appcheck/recaptchaenterprise/RecaptchaEnterpriseAppCheckProviderFactory.java

@@ -42,8 +42,17 @@ private RecaptchaEnterpriseAppCheckProviderFactory(@NonNull String siteKey) {
   /** Gets an instance of this class for installation into a {@link FirebaseAppCheck} instance. */
   @NonNull
   public static RecaptchaEnterpriseAppCheckProviderFactory getInstance(@NonNull String siteKey) {
-    return factoryInstances.computeIfAbsent(
-        siteKey, RecaptchaEnterpriseAppCheckProviderFactory::new);
+    RecaptchaEnterpriseAppCheckProviderFactory factory = factoryInstances.get(siteKey);
+    if (factory == null) {
+      synchronized (factoryInstances) {
+        factory = factoryInstances.get(siteKey);
+        if (factory == null) {
+          factory = new RecaptchaEnterpriseAppCheckProviderFactory(siteKey);
+          factoryInstances.put(siteKey, factory);
+        }
+      }
+    }
+    return factory;
   }
 
   @NonNull
@@ -56,6 +65,7 @@ public AppCheckProvider create(@NonNull FirebaseApp firebaseApp) {
           ProviderMultiResourceComponent component =
               firebaseApp.get(ProviderMultiResourceComponent.class);
           provider = component.get(siteKey);
+          provider.initializeRecaptchaClient();
         }
       }
     }

appcheck/firebase-appcheck-recaptchaenterprise/src/main/java/com/google/firebase/appcheck/recaptchaenterprise/internal/ProviderMultiResourceComponent.java

@@ -37,7 +37,17 @@ public final class ProviderMultiResourceComponent {
 
   @NonNull
   public RecaptchaEnterpriseAppCheckProvider get(@NonNull String siteKey) {
-    return instances.computeIfAbsent(siteKey, providerFactory::create);
+    RecaptchaEnterpriseAppCheckProvider provider = instances.get(siteKey);
+    if (provider == null) {
+      synchronized (instances) {
+        provider = instances.get(siteKey);
+        if (provider == null) {
+          provider = providerFactory.create(siteKey);
+          instances.put(siteKey, provider);
+        }
+      }
+    }
+    return provider;
   }
 
   @AssistedFactory

appcheck/firebase-appcheck-recaptchaenterprise/src/main/java/com/google/firebase/appcheck/recaptchaenterprise/internal/RecaptchaEnterpriseAppCheckProvider.java

@@ -89,6 +89,17 @@ public RecaptchaEnterpriseAppCheckProvider(
     this.recaptchaTasksClientTask = Tasks.forResult(recaptchaTasksClient);
   }
 
+  public void initializeRecaptchaClient() {
+    if (recaptchaTasksClientTask == null) {
+      synchronized (this) {
+        if (recaptchaTasksClientTask == null) {
+          Log.d(TAG, "Initializing RecaptchaTasksClient for siteKey: " + siteKey);
+          recaptchaTasksClientTask = Recaptcha.fetchTaskClient(application, siteKey);
+        }
+      }
+    }
+  }
+
   @NonNull
   @Override
   public Task<AppCheckToken> getToken() {
@@ -116,13 +127,6 @@ public Task<AppCheckToken> getToken() {
 
   @NonNull
   private Task<String> getRecaptchaEnterpriseAttestation() {
-    if (recaptchaTasksClientTask == null) {
-      synchronized (this) {
-        if (recaptchaTasksClientTask == null) {
-          recaptchaTasksClientTask = Recaptcha.fetchTaskClient(application, siteKey);
-        }
-      }
-    }
     return recaptchaTasksClientTask.continueWithTask(
         blockingExecutor,
         task -> {