[AuthorizeProduct]
    public IHttpActionResult Get (int id)
     {
       Product product = _repository.Get (id);
       if (product == null)
         {
          return NotFound();
         }
       return Ok(product);
     }

public class AuthorizeProductAttribute : AuthorizationFilterAttribute
    {
        public override void OnAuthorization(
        System.Web.Http.Controllers.HttpActionContext actionContext)
     {
        //do authorization
      }