private static readonly Regex _valueFormatMatch = new Regex(@"[0-9]", RegexOptions.Compiled);

using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Net.Http;
using System.Web;
using System.Web.Helpers;
using System.Web.Http.Controllers;
using System.Web.Http.Filters;
using System.Web.Mvc;
using ActionFilterAttribute = System.Web.Http.Filters.ActionFilterAttribute;

namespace NgxAntiforgeryWebApi.Providers
{
    public class XsrfCookieGeneratorAttribute : ActionFilterAttribute
    {
        public override void OnActionExecuted(HttpActionExecutedContext actionExecutedContext)
        {
            var xsrfTokenCookie = new HttpCookie("XSRF-TOKEN")
            {
                Value = ComputeXsrfTokenValue(),
                HttpOnly = false // Now JavaScript is able to read the cookie
            };
            HttpContext.Current.Response.AppendCookie(xsrfTokenCookie);
        }

        private string ComputeXsrfTokenValue()
        {
            string cookieToken, formToken;
            AntiForgery.GetTokens(null, out cookieToken, out formToken);
            return $"{cookieToken}:{formToken}";
        }
    }

    public class XsrfTokensValidationAttribute : ActionFilterAttribute
    {
        public override void OnActionExecuting(HttpActionContext actionContext)
        {
            IEnumerable<string> headerValues;
            if (!actionContext.Request.Headers.TryGetValues("X-XSRF-TOKEN", out headerValues))
            {
                actionContext.Response = new HttpResponseMessage(HttpStatusCode.BadRequest) { ReasonPhrase = "X-XSRF-TOKEN header is missing." };
                return;
            }

            if (headerValues == null)
            {
                actionContext.Response = new HttpResponseMessage(HttpStatusCode.BadRequest) { ReasonPhrase = "X-XSRF-TOKEN header value is empty." };
                return;
            }

            var xsrfTokensValue = headerValues.FirstOrDefault();
            if (string.IsNullOrEmpty(xsrfTokensValue) || !xsrfTokensValue.Contains(":"))
            {
                actionContext.Response = new HttpResponseMessage(HttpStatusCode.BadRequest) { ReasonPhrase = "X-XSRF-TOKEN header value is null." };
                return;
            }

            var values = xsrfTokensValue.Split(':');
            if (values.Length != 2)
            {
                actionContext.Response = new HttpResponseMessage(HttpStatusCode.BadRequest) { ReasonPhrase = "X-XSRF-TOKEN header value is malformed." };
                return;
            }

            var cookieToken = values[0];
            var formToken = values[1];

            try
            {
                AntiForgery.Validate(cookieToken, formToken);
            }
            catch (HttpAntiForgeryException ex)
            {
                actionContext.Response = new HttpResponseMessage(HttpStatusCode.BadRequest) {  ReasonPhrase = ex.Message };
            }
        }
    }
}