diff --git a/auth.php b/auth.php
new file mode 100644
index 0000000..cc2162b
--- /dev/null
+++ b/auth.php
@@ -0,0 +1,62 @@
+<?php
+session_start();
+
+header('Content-Type: application/json');
+
+require __DIR__ . '/vendor/autoload.php'; // Composer Autoloader
+
+use Kreait\Firebase\Factory;
+use Kreait\Firebase\Exception\Auth\InvalidToken;
+
+$response = ['status' => 'error', 'message' => 'Invalid request'];
+
+if ($_SERVER['REQUEST_METHOD'] === 'POST') {
+    $input = json_decode(file_get_contents('php://input'), true);
+
+    $action = $input['action'] ?? '';
+    $idToken = $input['idToken'] ?? '';
+
+    // Initialize Firebase Admin SDK
+    // IMPORTANT: Replace 'path/to/your/serviceAccountKey.json' with the actual path to your Firebase service account key file.
+    // This file contains your project's credentials and should be kept secure.
+    // You can download it from Firebase Console -> Project settings -> Service accounts -> Generate new private key.
+    try {
+        $factory = (new Factory())->withServiceAccount(__DIR__ . '/firebase-service-account.json');
+        $auth = $factory->createAuth();
+    } catch (\Exception $e) {
+        error_log('Firebase Admin SDK initialization error: ' . $e->getMessage());
+        $response = ['status' => 'error', 'message' => 'Server configuration error.'];
+        echo json_encode($response);
+        exit;
+    }
+
+
+    if ($action === 'signin' && !empty($idToken)) {
+        try {
+            $verifiedIdToken = $auth->verifyIdToken($idToken);
+            $uid = $verifiedIdToken->claims()->get('sub');
+            $email = $verifiedIdToken->claims()->get('email');
+            $displayName = $verifiedIdToken->claims()->get('name');
+
+            $_SESSION['user_id'] = $uid;
+            $_SESSION['user_email'] = $email;
+            $_SESSION['user_name'] = $displayName;
+            $_SESSION['is_logged_in'] = true;
+
+            $response = ['status' => 'success', 'message' => 'Sign-in successful.', 'user' => ['uid' => $uid, 'email' => $email, 'name' => $displayName]];
+        } catch (InvalidToken $e) {
+            $response = ['status' => 'error', 'message' => 'Invalid Firebase ID token.'];
+            error_log('Firebase ID token verification failed: ' . $e->getMessage());
+        } catch (\Exception $e) {
+            $response = ['status' => 'error', 'message' => 'Authentication failed.'];
+            error_log('General authentication error: ' . $e->getMessage());
+        }
+    } else if ($action === 'signout') {
+        session_unset();
+        session_destroy();
+        $response = ['status' => 'success', 'message' => 'Sign-out successful. Session destroyed.'];
+    }
+}
+
+echo json_encode($response);
+?>
diff --git a/firebase-service-account.json b/firebase-service-account.json
new file mode 100644
index 0000000..8a1d236
--- /dev/null
+++ b/firebase-service-account.json
@@ -0,0 +1,29 @@
+{ "type": "service_account", "project_id": "dululu-fe617", "private_key_id": "f994dbe9213123675911cb1556e73579f9a2d5b0", "private_key": "-----BEGIN PRIVATE KEY-----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+-----END PRIVATE KEY-----
+", "client_email": "firebase-adminsdk-fbsvc @dululu-fe617.iam.gserviceaccount.com", "client_id": "104495485400716482072", "auth_uri": "https://accounts.google.com/o/oauth2/auth", "token_uri": "https://oauth2.googleapis.com/token", "auth_provider_x509_cert_url": "https://www.googleapis.com/oauth2/v1/certs", "client_x509_cert_url": "https://www.googleapis.com/robot/v1/metadata/x509/firebase-adminsdk-fbsvc%40dululu-fe617.iam.gserviceaccount.com", "universe_domain": "googleapis.com" }
\ No newline at end of file
diff --git a/includes/firebase_config.php b/includes/firebase_config.php
new file mode 100644
index 0000000..399a154
--- /dev/null
+++ b/includes/firebase_config.php
@@ -0,0 +1,15 @@
+<?php
+// firebase_config.php
+// This file will hold your Firebase project configuration.
+// You need to replace the placeholder values with your actual Firebase project settings.
+// You can find these values in your Firebase project console under Project settings -> General -> Your apps.
+
+return [
+    'apiKey'            => 'AIzaSyCwEATlIVGKEvm-Ph1oH0-fOySmx7hBYkg',
+    'authDomain'        => 'dululu-fe617.firebaseapp.com',
+    'projectId'         => 'dululu-fe617',
+    'storageBucket'     => 'dululu-fe617.firebasestorage.app',
+    'messagingSenderId' => '553086833572',
+    'appId'             => '1:553086833572:web:2536751230886bd8552731',
+    'measurementId'     => 'G-5DJ9LXGSZZ' // Optional, if you use Google Analytics for Firebase
+];
diff --git a/index.php b/index.php
index 5bac7bf..3aacefd 100644
--- a/index.php
+++ b/index.php
@@ -1,6 +1,9 @@
 <?php
 declare(strict_types=1);
 require_once __DIR__ . '/db/config.php';
+require_once __DIR__ . '/includes/firebase_config.php';
+
+$firebaseConfig = require __DIR__ . '/includes/firebase_config.php';
 
 $delulus = [];
 try {
@@ -39,6 +42,90 @@ $projectTitle = 'Delulu is the New Sululu';
     <link rel="preconnect" href="https://fonts.gstatic.com" crossorigin>
     <link href="https://fonts.googleapis.com/css2?family=Poppins:wght@400;600;700&display=swap" rel="stylesheet">
     <link rel="stylesheet" href="assets/css/custom.css?v=<?php echo time(); ?>">
+
+    <script type="module">
+      // Import the functions you need from the SDKs you need
+      import { initializeApp } from "https://www.gstatic.com/firebasejs/10.12.2/firebase-app.js";
+      import { getAuth, GoogleAuthProvider, signInWithPopup, signOut, onAuthStateChanged } from "https://www.gstatic.com/firebasejs/10.12.2/firebase-auth.js";
+      // TODO: Add SDKs for Firebase products that you want to use
+      // https://firebase.google.com/docs/web/setup#available-libraries
+
+      // Your web app's Firebase configuration
+      const firebaseConfig = <?= json_encode($firebaseConfig) ?>;
+
+      // Initialize Firebase
+      const app = initializeApp(firebaseConfig);
+      const auth = getAuth(app);
+      const provider = new GoogleAuthProvider();
+
+      const authUi = document.getElementById('auth-ui');
+      const signInButton = document.getElementById('signInButton');
+
+      // Update UI based on auth state
+      onAuthStateChanged(auth, (user) => {
+        if (user) {
+          // User is signed in
+          authUi.innerHTML = `
+            <span class="navbar-text me-3">Welcome, \${user.displayName}</span>
+            <button id="signOutButton" class="btn btn-outline-danger">Sign Out</button>
+          `;
+          document.getElementById('signOutButton').addEventListener('click', () => {
+            signOut(auth).then(() => {
+              // Sign-out successful.
+              console.log('User signed out');
+            }).catch((error) => {
+              // An error happened.
+              console.error('Sign out error:', error);
+            });
+          });
+          // After successful sign-in, send ID token to backend for session management
+          user.getIdToken().then(idToken => {
+            fetch('auth.php', {
+              method: 'POST',
+              headers: {
+                'Content-Type': 'application/json',
+              },
+              body: JSON.stringify({ idToken: idToken, action: 'signin' }),
+            })
+            .then(response => response.json())
+            .then(data => {
+              if (data.status === 'success') {
+                console.log('Backend session established:', data.message);
+              } else {
+                console.error('Backend session error:', data.message);
+              }
+            })
+            .catch(error => {
+              console.error('Error sending token to backend:', error);
+            });
+          });
+
+        } else {
+          // User is signed out
+          authUi.innerHTML = `<button id="signInButton" class="btn btn-primary">Sign in with Google</button>`;
+          document.getElementById('signInButton').addEventListener('click', () => {
+            signInWithPopup(auth, provider)
+              .then((result) => {
+                // This gives you a Google Access Token. You can use it to access the Google API.
+                const credential = GoogleAuthProvider.credentialFromResult(result);
+                const token = credential.accessToken;
+                // The signed-in user info.
+                const user = result.user;
+                console.log('User signed in:', user.displayName);
+              }).catch((error) => {
+                // Handle Errors here.
+                const errorCode = error.code;
+                const errorMessage = error.message;
+                // The email of the user's account used.
+                const email = error.customData.email;
+                // The AuthCredential type that was used.
+                const credential = GoogleAuthProvider.credentialFromError(error);
+                console.error('Sign-in error:', errorMessage);
+              });
+          });
+        }
+      });
+    </script>
 </head>
 <body>
 
@@ -50,8 +137,9 @@ $projectTitle = 'Delulu is the New Sululu';
             </button>
             <div class="collapse navbar-collapse" id="navbarNav">
                 <ul class="navbar-nav ms-auto">
-                    <li class="nav-item">
-                        <a class="btn btn-primary" href="#">Sign in with Google</a>
+                    <li class="nav-item" id="auth-ui">
+                        <!-- Authentication UI will be rendered here -->
+                        <button id="signInButton" class="btn btn-primary">Sign in with Google</button>
                     </li>
                 </ul>
             </div>