Explain the concept of middleware in ASP.NET and its role in processing HTTP requests.

Middleware in ASP.NET is composed of components that handle HTTP requests and responses in the processing pipeline. Each middleware can perform actions before and after passing control to the next component.

The role of middleware:

• Handling authentication and authorization
• Logging requests
• Error handling
• Caching
• Modifying requests or responses

Example of simple middleware in C#:

public class SimpleMiddleware
{
    private readonly RequestDelegate _next;

    public SimpleMiddleware(RequestDelegate next)
    {
        _next = next;
    }

    public async Task InvokeAsync(HttpContext context)
    {
        // Actions before passing to the next middleware
        Console.WriteLine("Request incoming");

        await _next(context);

        // Actions after the next middleware has executed
        Console.WriteLine("Response outgoing");
    }
}

Middleware is registered in the Configure method of the Startup class using app.UseMiddleware<SimpleMiddleware>();.