auth: Implement RecaptchaEnterprise and AppCheck

* Dynamically loads reCAPTCHA enterprise script
* This avoids key duplication and makes future updates easier to manage.

auth/config.ts

@@ -10,3 +10,7 @@ export const firebaseConfig = {
   appId: 'APP_ID',
   measurementId: 'G-MEASUREMENT_ID',
 };
+
+// Your web app's ReCaptcha Enterprise Site-Key
+// https://firebase.google.com/docs/app-check/web/recaptcha-enterprise-provider#project-setup
+export const reCaptchaSiteKey = 'RECAPTCHA_SITE_KEY'

auth/mfa-password-enterprise.html

@@ -338,7 +338,6 @@ <h2 class="mdl-card__title-text">
       </main>
     </div>
 
-    <script src="https://www.google.com/recaptcha/api.js"></script>
-    <script type="module" src="mfa-password.ts"></script>
+    <script type="module" src="mfa-password-enterprise.ts"></script>
   </body>
 </html>

auth/mfa-password-enterprise.ts

@@ -23,6 +23,8 @@
 // Hence, we do not connect to the emulator in this example.
 
 import { initializeApp } from 'firebase/app';
+import { initializeAppCheck, ReCaptchaEnterpriseProvider } from "firebase/app-check";
+
 import {
   MultiFactorInfo,
   MultiFactorResolver,
@@ -33,19 +35,42 @@ import {
   createUserWithEmailAndPassword,
   getAuth,
   getMultiFactorResolver,
+  initializeRecaptchaConfig,
   multiFactor,
   onAuthStateChanged,
   sendEmailVerification,
   sendPasswordResetEmail,
   signInWithEmailAndPassword,
   signOut,
 } from 'firebase/auth';
-import { firebaseConfig } from './config';
-
-initializeApp(firebaseConfig);
+import { firebaseConfig, reCaptchaSiteKey } from './config';
+
+// Dynamically load the reCAPTCHA enterprise script
+const script = document.createElement('script');
+script.src = `https://www.google.com/recaptcha/enterprise.js?render=${reCaptchaSiteKey}`;
+script.async = true;
+script.defer = true;
+document.head.appendChild(script);
+
+const app = initializeApp(firebaseConfig);
+
+// Initialize App Check
+initializeAppCheck(app, {
+  provider: new ReCaptchaEnterpriseProvider(reCaptchaSiteKey),
+  // Optional: set to true if you want to allow App Check to run on unsupported browsers
+  isTokenAutoRefreshEnabled: true
+});
 
 const auth = getAuth();
 
+initializeRecaptchaConfig(auth)
+  .then(() => {
+    console.log("Recaptcha Enterprise Config Initialization successful.")
+  })
+  .catch((error) => {
+    console.error("Recaptcha Enterprise Config Initialization failed with " + error)
+  });
+
 let mfaResolver: MultiFactorResolver | null = null;
 let phoneVerificationId: string | null = null;
 let recaptchaVerifier: RecaptchaVerifier | null = null;