public void Configuration(IAppBuilder app)
{
    app.Use(async (ctx, next) =>
    {
        Console.WriteLine("preprocessing");
        await next();
        Console.WriteLine("postprocessing");
    });

    app.Run(async ctx =>
    {
        Console.WriteLine(ctx.Request.Method);
        Console.WriteLine(ctx.Request.Uri);
        await ctx.Response.WriteAsync("<h1>Hello OWIN and Katana</h1>");
    });
}