Umbraco CORS

startup.cs

// Don't forget to update Global.asax to point to this class!!

namespace UmbracoCms._7._3._4.App_Start
{
    using System;
    using System.Web.Http;
    using System.Web.Http.Cors;

    /// <summary>
    /// 
    /// </summary>
    public class MyCmsApplication : Umbraco.Web.UmbracoApplication
    {
        /// <summary>
        /// Called when [application starting].
        /// </summary>
        /// <param name="sender">The sender.</param>
        /// <param name="e">The <see cref="EventArgs"/> instance containing the event data.</param>
        protected override void OnApplicationStarting(object sender, EventArgs e)
        {
            base.OnApplicationStarting(sender, e);
            GlobalConfiguration.Configure(WebApiConfig.Register);
        }
    }

    /// <summary>
    /// 
    /// </summary>
    public static class WebApiConfig
    {
        /// <summary>
        /// Registers the specified configuration.
        /// </summary>
        /// <param name="config">The configuration.</param>
        public static void Register(HttpConfiguration config)
        {
            var corsAttr = new EnableCorsAttribute("*", "*", "*");
            config.EnableCors(corsAttr);
        }
    }
}

Web.config

<httpProtocol>
  <customHeaders>
    <remove name="X-Powered-By" />
    <add name="Access-Control-Allow-Methods" value="GET, PUT, POST, DELETE, HEAD" />
    <add name="Access-Control-Allow-Headers" value="Origin, X-Requested-With, Content-Type, Accept" />
  </customHeaders>
</httpProtocol>

Cannot get it working. Could ya help me?