Very basic CORS HttpModule

CorsModule.cs

using System;
using System.Web;

namespace MyOtherSite
{
    public class CorsModule : IHttpModule
    {
        public void Init(HttpApplication application)
        {
            application.BeginRequest += ApplicationOnBeginRequest;
        }

        private void ApplicationOnBeginRequest(object sender, EventArgs eventArgs)
        {
            var application = (HttpApplication) sender;
            if (!CheckCors(application.Context))
            {
                application.Context.Response.StatusCode = 403;
                application.CompleteRequest();
            }
        }

        private static bool CheckCors(HttpContext context)
        {
            var origin = context.Request.Headers["Origin"];
            if (origin != "https://mysite.com")
            {
                return false;
            }
            context.Response.AddHeader("Access-Control-Allow-Origin", origin);
            context.Response.AddHeader("Access-Control-Allow-Credentials", "true");
            context.Response.AddHeader("Access-Control-Allow-Methods", "GET,POST,PUT,PATCH,DELETE");
            return true;
        }

        public void Dispose()
        {
        }
    }
}

Getting No 'Access-Control-Allow-Origin' header is present on the requested resource. Origin 'http://myhost.com' is therefore not allowed access.
Code Snippet:
response.AddHeader("Access-Control-Allow-Headers", "Origin, Content-Type, Accept");
response.AddHeader("Access-Control-Allow-Origin", origin);
response.AddHeader("Access-Control-Request-Methods", "POST,GET");
response.AddHeader("Access-Control-Allow-Credentials", "true");