Add AntiForgeryToken to Response Header

AddCsrfTokenHeader

    public class AddCsrfTokenHeader:ActionFilterAttribute
    {
        public override void OnResultExecuted(ResultExecutedContext filterContext)
        {
            HttpCookie cookie = null;
            
            // First, try and get cookie from Response. That'll be a new cookie
            if (filterContext.HttpContext.Response.Cookies.AllKeys.Contains(AntiForgeryConfig.CookieName))
            {
                cookie = filterContext.HttpContext.Response.Cookies.Get(AntiForgeryConfig.CookieName);
            }

            // If no new cookie, try and get from Request. Existing cookie is valid.
            if (cookie == null || String.IsNullOrEmpty(cookie.Value))
            {
                if (filterContext.HttpContext.Request.Cookies.AllKeys.Contains(AntiForgeryConfig.CookieName))
                {
                    cookie = filterContext.HttpContext.Request.Cookies.Get(AntiForgeryConfig.CookieName);
                }
            }

            // If there's any cookie, then make a token for the header from it
            if (cookie != null && !String.IsNullOrEmpty(cookie.Value))
            {
                string cookieToken = cookie.Value;
                string formToken;
                string nullToken;

                AntiForgery.GetTokens(cookieToken, out nullToken, out formToken);
                filterContext.HttpContext.Response.AddHeader("X-RequestVerificationToken", formToken);
            }

            base.OnResultExecuted(filterContext);

        }
    }

Useful for load testing an ASP.NET MVC app with loader.io and AntiForgeryTokens.