Last-Modified Header in Asp.net Core MVC

public class YourController : Controller
{
    public ActionResult MyPage(string id)
    {
        var entity = _db.Get(id);
        var headerValue = context.HttpContext.Request.Headers['If-Modified-Since'];
        if (headerValue != null)
        {
            var modifiedSince = DateTime.Parse(headerValue).ToLocalTime();
            if (modifiedSince >= entity.UpdatedAt)
            {
               context.HttpContext.Response.StatusCode = 304;
               return new EmptyResult();
            }
        }

        // page has been changed.
        // generate a view ...

        // .. and set last modified in the date format specified in the HTTP rfc.
        context.HttpContext.Response.AddHeader('Last-Modified', entity.UpdatedAt.ToUniversalTime().ToString("R"));
    }
}