TransformMicroservice.cs

    using System;
    using System.IO;
    using System.Net;
    using System.Threading.Tasks;
    using Microsoft.Owin;
    using Nowin;
    using AppFunc = System.Func<System.Collections.Generic.IDictionary<string, object>, System.Threading.Tasks.Task>;

    internal class Program
    {
        private static void Main(string[] args)
        {
            Func<StreamReader, Task<string>> transform = async reader => await reader.ReadToEndAsync();

            AppFunc appFunc = async env =>
            {
                var context = new OwinContext(env);

                if(context.Request.Method.Equals("POST", StringComparison.OrdinalIgnoreCase))
                {
                    using (var writer = new StreamWriter(context.Response.Body))
                    using (var reader = new StreamReader(context.Request.Body))
                    {
                        await writer.WriteAsync(await transform(reader));
                    }
                    return;
                }

                context.Response.StatusCode = 400;
                context.Response.ReasonPhrase = "Bad Request";
            };

            var server = ServerBuilder.New()
                .SetEndPoint(new IPEndPoint(IPAddress.Any, 8888))
                .SetOwinApp(appFunc)
                .Build();

            using(server)
            {
                server.Start();

                Console.WriteLine("Server running on http://localhost:8888");
                Console.WriteLine("hit to stop");
                Console.ReadLine();
            }
        }
    }