OwinContextなしで、KatanaのStartupを利用

HelloApp.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Threading.Tasks;
using System.IO;
using System.Text;

namespace OwinSample
{
    public class HelloApp
    {
        string message;
        public HelloApp(object next, string message)
        {
            this.message = message;
        }

        public Task Invoke(IDictionary<string, object> env)
        {
            var headers = env["owin.ResponseHeaders"] as IDictionary<string, string[]>;
            headers["Content-type"] = new string[]{"text/plain;charset=utf-8"};
            var contents = Encoding.UTF8.GetBytes(message);
            var body = env["owin.ResponseBody"] as Stream;
            return body.WriteAsync(contents, 0, contents.Length);
        }
    }
}

StartApp.cs

using System;
using System.Threading.Tasks;
using Microsoft.Owin;
using Owin;

[assembly: OwinStartup(typeof(OwinSample.Startup))]

namespace OwinSample
{
    public class Startup
    {
        public void Configuration(IAppBuilder app)
        {
            app.Use<HelloApp>("Hello, world!");
        }
    }

}