In ASP.NET Core 2.2, middleware is configured in the Startup class:

public void Configure(IApplicationBuilder app, IHostingEnvironment env)
{
    app.Use(async (context, next) => 
    {
        context.Response.ContentType = "text/html; charset=utf-8";
        await context.Response.WriteAsync("<h3>Middleware1 start</h3>");
        await next();
        await context.Response.WriteAsync("<h3>Middleware1 end</h3>");
    });
    
    app.Use(async (context, next) => 
    {
        await context.Response.WriteAsync("<h3>Middleware2 start</h3>");
        await next();
        await context.Response.WriteAsync("<h3>Middleware2 end</h3>");
    });

    app.Run(async context => 
        await context.Response.WriteAsync("Pipeline complete"));
}

Understanding Middleware Architecture

The core middleware mechanism works through delegate composition:

public class MiddlewarePipeline
{
    private readonly List<Func<RequestDelegate, RequestDelegate>> _components = 
        new List<Func<RequestDelegate, RequestDelegate>>();

    public void Use(Func<RequestDelegate, RequestDelegate> middleware)
    {
        _components.Add(middleware);
    }

    public RequestDelegate Build()
    {
        RequestDelegate pipeline = context => 
        {
            context.Response.StatusCode = 404;
            return Task.CompletedTask;
        };

        foreach (var component in _components.Reverse())
        {
            pipeline = component(pipeline);
        }
        
        return pipeline;
    }
}

Custom Middleware Implementation Example

Here's a simplified middleware implementation:

public class CustomMiddleware
{
    private List<Func<MiddlewareDelegate, MiddlewareDelegate>> _middleware = 
        new List<Func<MiddlewareDelegate, MiddlewareDelegate>>();

    public void Add(Func<MiddlewareDelegate, MiddlewareDelegate> middleware)
    {
        _middleware.Add(middleware);
    }

    public MiddlewareDelegate BuildPipeline()
    {
        MiddlewareDelegate pipeline = msg => Task.CompletedTask;
        
        foreach (var component in _middleware.Reverse())
        {
            pipeline = component(pipeline);
        }
        
        return pipeline;
    }
}

public delegate Task MiddlewareDelegate(string message);

This demonstrates the fundamental pattern of ASP.NET Core middleware execution.