Update OAuth2.md

OAuth2.md

@@ -463,27 +463,94 @@ Authorization: Bearer ya29.a0AfH6SMC8Op6zXZkHi2XITkDoOVzYXt3hTY6sny54UlWlxrnKlX5
 <summary><h3>Backend GET Code</h3></summary>
 
 ```js
-app.get('/api/user-profile', async (req, res) => {
-  const accessToken = req.headers['authorization'].split(' ')[1]; // Extract token from Authorization header
-  
+const express = require('express');
+const axios = require('axios');
+
+const app = express();
+app.use(express.json()); // To parse JSON bodies
+
+const clientId = 'YOUR_GOOGLE_CLIENT_ID'; // Google Client ID
+const clientSecret = 'YOUR_GOOGLE_CLIENT_SECRET'; // Google Client Secret
+const redirectUri = 'https://xorismesiti.gr/api/auth/callback'; // Must match the one used in frontend
+
+// Function to validate the access token by making a request to the Google user info endpoint
+const validateAccessToken = async (accessToken) => {
   try {
     const response = await axios.get('https://www.googleapis.com/oauth2/v3/userinfo', {
       headers: {
         Authorization: `Bearer ${accessToken}`,
       },
     });
-    
-    // Send the user profile data to the frontend
-    res.json(response.data);
+
+    // If this succeeds, the token is valid
+    return response.data; // Return the user data
   } catch (error) {
-    console.error('Error fetching user profile:', error);
-    res.status(500).json({ error: 'Failed to fetch user profile' });
+    // If the request fails (token is invalid or expired), throw an error
+    throw new Error('Invalid or expired access token');
   }
+};
+
+// Example route for fetching the user profile
+app.get('/api/user-profile', async (req, res) => {
+  const accessToken = req.headers['authorization']?.split(' ')[1]; // Extract token from Authorization header
+  
+  if (!accessToken) {
+    return res.status(400).json({ error: 'No access token provided' });
+  }
+
+  try {
+    // Validate the access token by fetching user info from Google
+    const userData = await validateAccessToken(accessToken);
+
+    // Send the user profile data to the frontend
+    res.json(userData);
+  } catch (error) {
+    // Handle invalid or expired token
+    console.error('Error validating access token:', error);
+    res.status(401).json({ error: 'Invalid or expired access token' });
+  }
+});
+
+// Start the server
+app.listen(3000, () => {
+  console.log('Server running on http://localhost:3000');
 });
 ```
 
 </details>
 
+<details>
+<summary><h3>Front GET Code</h3></summary>
+
+```js
+// After receiving the token, store it in the frontend (e.g., localStorage or context)
+localStorage.setItem('access_token', response.access_token);
+
+// Use it to make authenticated API requests to the backend
+fetch('/api/user-profile', {
+  headers: {
+    'Authorization': `Bearer ${localStorage.getItem('access_token')}`,
+  },
+})
+  .then(response => {
+    if (response.status === 401) {
+      // Handle token expiration or invalid token
+      console.error('Access token expired or invalid. Please log in again.');
+      // Optionally, redirect to login page or refresh token
+    } else {
+      return response.json();
+    }
+  })
+  .then(data => {
+    // Handle user data
+    console.log(data);
+  })
+  .catch(error => {
+    console.error('Error fetching user profile:', error);
+  });
+```
+</details>
+
 <br><br><br>