Middleware that rejoins the parent pipeline

UseMapMiddleware.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using Microsoft.AspNet.Builder;
using Microsoft.AspNet.Http;

namespace WebApplication58
{
    public class MapUseMiddleware
    {
        private readonly RequestDelegate _childPipeline;

        public MapUseMiddleware(RequestDelegate next, IApplicationBuilder subBuilder)
        {
            subBuilder.Use(subNext =>
            {
                return ctx => next(ctx);
            });

            _childPipeline = subBuilder.Build();
        }

        public Task Invoke(HttpContext httpContext)
        {
            return _childPipeline(httpContext);
        }
    }

    // Extension method used to add the middleware to the HTTP request pipeline.
    public static class MapUseMiddlewareExtensions
    {
        public static IApplicationBuilder UseMapMiddleware(this IApplicationBuilder builder, Action<IApplicationBuilder> configuration)
        {
            var branchBuilder = builder.New();
            configuration(branchBuilder);

            return builder.UseMiddleware<MapUseMiddleware>(branchBuilder);
        }
    }
}