Can I implement custom CORS headers manually in Node.js without using the `cors` package? If so, how?

Yes, you can manually implement CORS headers in Node.js without the `cors` package, though it requires more boilerplate code. You would typically create a middleware function that sets the appropriate `Access-Control-*` headers on every response. You also need to explicitly handle preflight (OPTIONS) requests. Example for Express: `app.use((req, res, next) => { res.setHeader('Access-Control-Allow-Origin', 'http://localhost:3000'); res.setHeader('Access-Control-Allow-Methods', 'GET, POST, PUT, DELETE, OPTIONS'); res.setHeader('Access-Control-Allow-Headers', 'Content-Type, Authorization'); res.setHeader('Access-Control-Allow-Credentials', 'true'); if (req.method === 'OPTIONS') { return res.sendStatus(200); } next(); });` This approach gives fine-grained control but needs careful handling for all edge cases like `Max-Age` and dynamic origins.