1 using System;
 2 using System.Threading.Tasks;
 3 using Microsoft.Owin;
 4 using Owin;
 5 using System.Web.Http;
 6 
 7 [assembly: OwinStartup(typeof(FirstOwinWebApi.Startup))]
 8 
 9 namespace FirstOwinWebApi
10 {
11     public class Startup
12     {
13         public void Configuration(IAppBuilder app)
14         {
15             HttpConfiguration config = new HttpConfiguration();
16 
17             // Web API routes
18             config.MapHttpAttributeRoutes();
19 
20             //WebApiConfig.Register(config);
21 
22             app.UseWebApi(config);
23         }
24     }
25 }

 1 using System;
 2 using System.Collections.Generic;
 3 using System.Linq;
 4 using System.Net;
 5 using System.Net.Http;
 6 using System.Web.Http;
 7 
 8 namespace FirstOwinWebApi.Controllers
 9 {
10     [RoutePrefix("api/HelloWorld")]
11     public class HelloWorldController : ApiController
12     {
13         [Route("")]
14         public IHttpActionResult Post()
15         {
16 
17             return Ok<string>("Hello World");
18 
19         }
20 
21     }
22 }