ASP.NET Core middleware is a powerful feature that allows developers to add functionality to specific routes in their web applications. However, sometimes you may want to restrict middleware to certain routes to improve your application’s security and performance. In this blog post, we’ll explore how to restrict middleware in ASP.NET Core by using the `builder.UseWhen()` method. We’ll provide an example of how to restrict middleware to a specific route and explain how to implement this functionality in your own applications. By the end of this post, you’ll have a better understanding of how to use middleware in ASP.NET Core and how to restrict it to specific routes for better security and performance.