A sliding cache implementation... that still expires after 1 second even with requests every 300ms

TestCacheController.cs

using System;
using System.Net;
using System.Net.Http;
using System.Web;
using System.Web.Caching;
using System.Web.Http;

namespace Web.Controllers
{
  public class TestCacheController : ApiController
  {
    public HttpResponseMessage Get()
    {
      const string cacheKey = "MyCacheKey";
      var cacheValue = HttpRuntime.Cache.Get(cacheKey);

      // Value is not in cache, create the item and allow sliding expiration so it keeps extending
      if (cacheValue == null)
      {
        HttpRuntime.Cache.Insert(cacheKey, string.Empty, null, Cache.NoAbsoluteExpiration, TimeSpan.FromSeconds(1));
        return Request.CreateResponse(HttpStatusCode.OK);
      }

      // Item was in cache so return forbidden
      return Request.CreateResponse(HttpStatusCode.Forbidden);
    }
  }
}