feat(backend): Integrate CORS policy

backend/app.js

@@ -25,6 +25,27 @@ app.use(express.json());
 app.use(express.urlencoded({ extended: true }));
 app.use(cookieParser());
 
+// CORS Configuration
+app.options("*", function (req, res, next) {
+  res.setHeader(
+    "Access-Control-Allow-Origin",
+    "https://spend-smart-dev.vercel.app"
+  );
+  res.setHeader("Access-Control-Allow-credentials", true);
+  res.setHeader("Access-Control-Allow-Headers", "Content-Type");
+  res.setHeader("Access-Control-Allow-Methods", "GET, POST, PUT, DELETE");
+  next();
+});
+app.use(function (req, res, next) {
+  const origin = req.header.origin;
+  const allowedOrigins = ["https://spend-smart-dev.vercel.app"];
+  if (allowedOrigins.includes(origin)) {
+    next();
+  } else {
+    res.status(404).json({ error: "Blocked by CORS!" });
+  }
+});
+
 // Routes
 app.use("/api/v1/users", userRoutes);
 app.use("/api/v1/incomes", authenticateUser, incomeRoutes);