How do I set the Access-Control-Allow-Origin header on the server?

The method for setting the `Access-Control-Allow-Origin` header depends on your server-side technology. For example, in Node.js with Express, you would use middleware like `cors` or configure your server to send the header manually. In Apache, you'd modify the `.htaccess` file. In other frameworks, consult the documentation for your specific server-side language.