SomeController.cs

using System;
using System.Net;
using System.Web.Mvc;
using Mvc.Jsonp;

namespace My.Controllers
{
    [AuthFilter]
    public class SomeController : JsonpControllerBase
    {
        public JsonpResult GetAllItems(string callback)
        {
            var items = MyItemRepository.GetAllItems();
            return Jsonp(items, callback, JsonRequestBehavior.AllowGet);
        }
    }
}