Implement session-based authentication and add logout functionality

Fix #15

middleware/auth.js

@@ -1,15 +1,10 @@
 const basicAuth = require('basic-auth');
 
 const auth = (req, res, next) => {
-    const user = basicAuth(req);
-    const username = process.env.AUTH_USERNAME; // Use environment variables
-    const password = process.env.AUTH_PASSWORD; // Use environment variables
-
-    if (user && user.name === username && user.pass === password) {
+    if (req.session && req.session.user) {
         return next();
     } else {
-        res.set('WWW-Authenticate', 'Basic realm="401"');
-        return res.status(401).send('Authentication required.');
+        res.status(401).send('Authentication required.');
     }
 };