backend code refactoring

backend/middleware/index.js

@@ -0,0 +1,7 @@
+module.exports = function (req, res, next) {
+  res.header ('Access-Control-Allow-Origin', '*');
+  res.header ('Access-Control-Allow-Headers', 'Origin, Content-Type');
+  res.header ('Access-Control-Allow-Methods', 'GET, POST, OPTIONS');
+  res.header ('Access-Control-Allow-Credentials', 'true');
+  next ();
+};