如何在mvc4中禁用对生产服务器外部的Sitemap.xml文件的访问？

public class RobotsController : Controller
{
    public ActionResult Index()
    {
        Response.ContentType = "text/plain";
        return Content("User-agent: *\nDisallow: /Sitemap.xml");
    }
}

protected void Application_Start()
{
    // 其他代码...

    RouteTable.Routes.MapRoute(
        name: "Robots",
        url: "Robots.txt",
        defaults: new { controller = "Robots", action = "Index" }
    );
}

<system.webServer>
  <rewrite>
    <rules>
      <rule name="Redirect Sitemap.xml to Robots.txt" stopProcessing="true">
        <match url="^Sitemap.xml$" />
        <action type="Rewrite" url="/Robots.txt" />
      </rule>
    </rules>
  </rewrite>
</system.webServer>