Explain the middleware pipeline in ASP.NET Core

The middleware pipeline in ASP.NET Core is a series of components that handle HTTP requests and responses. Each middleware component can:

• Process an incoming request before passing it to the next component
• Process the outgoing response after the next component has executed
• Short-circuit the pipeline by not calling the next middleware

Key characteristics:

• Middleware components are executed in the order they are added
• Each component can perform operations before and after the next component
• Built using the Use, Run, and Map extension methods

Example:

public void Configure(IApplicationBuilder app)
{
    // Middleware 1
    app.Use(async (context, next) =>
    {
        // Do work before next middleware
        await next.Invoke();
        // Do work after next middleware
    });

    // Middleware 2
    app.UseRouting();
    app.UseAuthentication();
    app.UseAuthorization();
    
    // Terminal middleware
    app.UseEndpoints(endpoints =>
    {
        endpoints.MapControllers();
    });
}

Common middleware order:

1. Exception handling
2. HTTPS redirection
3. Static files
4. Routing
5. Authentication
6. Authorization
7. Endpoints