internal static User GetUserByID(int userID)
        {
            string Key = "User-" + userID;

            if (HttpContext.Current.Cache[Key] == null)
            {
                // cache is empty - populate from DB
                var user = new User(UserManager.GetUserInfoByID(userID));

                // store in cache
                HttpContext.Current.Cache.Insert(Key, user, null, DateTime.Now.AddMinutes(5), Cache.NoSlidingExpiration);
            }

            // return data from cache
            return HttpContext.Current.Cache[Key] as User;
        }