How do I enable CORS in C# web-api 2?

You can enable Cors in your web api project, by taking following steps:

1. "Install-Package Microsoft.AspNet.WebApi.Cors" from NuGet Package Manager console
2. Once the above Package is installed, open the file App_Start/WebApiConfig.cs. Add the following code to the WebApiConfig.Register method
   

    public static void Register(HttpConfiguration config)
           {
               //add to enable cors
               config.EnableCors(cors);
              
   
               //old code, route config etc.
           }?

3. Once done, you can add "[EnableCORS]" attribute above Web-API Controller or Method, for example
   

   using System.Web.Http.Cors; //add namespace
   
   namespace WebService.Controllers
   {
       [EnableCors(origins: "http://example.com", headers: "*", methods: "*")]
       public class SampleController : ApiController
       {
           // your API Controller code here
       }
   }?

4. You can enable CORS globally also, using the following code in your WebApiConfig.cs
   

    public static class WebApiConfig
       {
           public static void Register(HttpConfiguration config)
           {    
              //enable cors globally
               var cors = new EnableCorsAttribute("www.example.com", "*", "*");
               config.EnableCors(cors);
           }
       }?

Source: Enabling CORS in IIS (Various possible methods)

I have found one more way, which works fine, but it doesn't allow you do define CORS on controller basis.

You can use the below code in your web.config to enable CORS through out your application

<system.webServer>
    <httpProtocol>
        <customHeaders>
            <add name="Access-Control-Allow-Origin" value="*" />
        </customHeaders>
    </httpProtocol>
</system.webServer>

One more disadvantage of this using approach is it causes the header to be included in every response from your api server.