Resolved: Enable CORS on OWIN the right way

I was having difficulty, probably like you, trying to figure out how to get CORS working on a OWIN self-hosted application.  There were so many answers posted, but seemed like so many of them were based on older versions of Visual Studio / .NET.

Here is what I finally found to work for me; hopefully this will help you as well.  This is as of Visual Studio 2015 in early March 2017.

1. Add nuget packages to the web api project:
1. Microsoft.AspNet.WebApi.Cors
2. Microsoft.Owin.Cors (this will also install Microsoft.AspNet.Cors)
   
2. Modify startup.cs, Configuration(IAppBuilder app), add this line:
   
   app.UseCors(CorsOptions.AllowAll);
   
   and add it before the line:
   
   app.UseWebApi(config);
   
3. Add the following attribute on my web api controller class:
   
   [EnableCors("*", "*", "*")]
   

These three steps got things finally working.