public class StockQuoteController : SitecoreController {
    private IStockQuoteAgent _stockQuoteAgent;

    public StockQuoteController(IStockQuoteAgent stockQuoteAgent) {
        _stockQuoteAgent = stockQuoteAgent;
    }

    [OutputCache(CacheProfile = "StockQuoteCacheProfile")]
    [HttpPost]
    public JsonResult GetStockPrice() {
        ...
    }
}

<caching>
  <outputCache enableOutputCache="true" enableFragmentCache="true" sendCacheControlHeader="true" omitVaryStar="false"></outputCache>
  <outputCacheSettings>
    <outputCacheProfiles>
      <add name="StockQuoteCacheProfile" duration="1800" varyByParam="none" location="ServerAndClient" />
    </outputCacheProfiles>
  </outputCacheSettings>
</caching>