use IHttpHandler and HttpClient to Create Request Proxy For another Site

Handler.cs

using System;
using System.Configuration;
using System.IO;
using System.Net;
using System.Net.Http;
using System.Net.Http.Headers;
using System.Text;
using System.Web;
namespace Console.handler
{
    /// <summary>
    ///     Handler 的摘要说明
    /// </summary>
    public class Handler : IHttpHandler
    {
        public static readonly string TargetUrl ="http://"+ ConfigurationManager.AppSettings["JBPMHost"]+ ":"+ConfigurationManager.AppSettings["JBPMPort"]+ConfigurationManager.AppSettings["JBPMRoot"];
        public static readonly string TargetHost = ConfigurationManager.AppSettings["JBPMHost"] + ":" + ConfigurationManager.AppSettings["JBPMPort"] + ConfigurationManager.AppSettings["JBPMRoot"];
        public void ProcessRequest(HttpContext context)
        {
            try
            {
                HttpClientVersion(context);
            }
            catch (HttpUnSuccessException ex)
            {
                context.Response.StatusCode = ex.StatusCode;
                context.Response.Write(ex.ResponseText);
            }
               
        }
        public bool IsReusable => false;
        public void HttpClientVersion(HttpContext context)
        {
            var url = context.Request.RawUrl;
            url = url.TrimStart("/workflow");
            url = url.TrimStart("/editor");
            url = url.TrimStart("/idm");
            url ="http://admin:test@"+ TargetHost + url;
            var verbMethod = context.Request.HttpMethod;
            var handler = new HttpClientHandler {CookieContainer = new CookieContainer()};
            using (var httpClient = new HttpClient(handler))
            {
                var responseText = string.Empty;
                ComposeRequestEnv(httpClient, context, handler);
                if (verbMethod == "GET")
                {
                    var responseMessage = httpClient.GetAsync(url).Result;
                    if (responseMessage.StatusCode == HttpStatusCode.Unauthorized)
                    {
                        throw  new HttpUnSuccessException(401, "");
                    }
                    try
                    {
                        responseText = responseMessage.Content.ReadAsStringAsync().Result;
                        responseMessage.EnsureSuccessStatusCode();
                    }
                    catch (Exception ex)
                    {
                        throw new HttpUnSuccessException((int)responseMessage.StatusCode, responseText);
                    }
                   
                    var stream = responseMessage.Content.ReadAsStreamAsync().Result;
                    stream.CopyTo(context.Response.OutputStream);
                    if (responseMessage.Content.Headers.ContentType?.MediaType != null)
                        context.Response.ContentType = responseMessage.Content.Headers.ContentType.MediaType;
                    return;
                }
                MediaTypeHeaderValue mediaType;
                var streamContent = new StreamContent(context.Request.InputStream);
                if (MediaTypeHeaderValue.TryParse(context.Request.ContentType, out mediaType))
                    streamContent.Headers.ContentType = mediaType;
                HttpResponseMessage response = null;
                if (verbMethod == "POST")
                    response = httpClient.PostAsync(url, streamContent).Result;
                else if (verbMethod == "DELETE")
                    response = httpClient.DeleteAsync(url).Result;
                else if (verbMethod == "PUT")
                    response = httpClient.PutAsync(url, streamContent).Result;
                if (response.StatusCode == HttpStatusCode.Unauthorized)
                {
                    throw new HttpUnSuccessException(401,"");
                }
                try
                {
                    responseText = response.Content.ReadAsStringAsync().Result;
                    response.EnsureSuccessStatusCode();
                }
                catch (Exception ex)
                {
                    throw new HttpUnSuccessException((int)response.StatusCode, responseText);
                }
                if (response.Content.Headers.ContentType?.MediaType != null)
                    context.Response.ContentType = response.Content.Headers.ContentType.MediaType;
                var responseStream = response.Content.ReadAsStreamAsync().Result;
                responseStream.CopyTo(context.Response.OutputStream);
                var responseCookies = handler.CookieContainer.GetCookies(new Uri(TargetUrl));
                for (var i = 0; i < responseCookies.Count; i++)
                {
                    var ck = new HttpCookie(responseCookies[i].Name, responseCookies[i].Value);
                    context.Response.Cookies.Remove(ck.Name);
                    context.Response.Cookies.Add(ck);
                }
            }
        }
        private static void ComposeRequestEnv(HttpClient httpClient, HttpContext context, HttpClientHandler handler)
        {
            var cookies = context.Request.Cookies;
            httpClient.DefaultRequestHeaders.Add("User-Agent",
                "Mozilla/5.0 (compatible; MSIE 10.0; Windows NT 6.2; WOW64; Trident / 6.0)");
            httpClient.DefaultRequestHeaders.Host = ConfigurationManager.AppSettings["JBPMHost"];
            httpClient.DefaultRequestHeaders.Connection.ParseAdd("keep-alive");
            httpClient.DefaultRequestHeaders.Pragma.ParseAdd("no-cache");
            httpClient.DefaultRequestHeaders.Accept.ParseAdd("application/json, text/plain, */*");
            httpClient.DefaultRequestHeaders.CacheControl = new CacheControlHeaderValue
            {
                NoCache = true,
                NoStore = true,
                MustRevalidate = true
            };
            httpClient.DefaultRequestHeaders.AcceptEncoding.ParseAdd("gzip, deflate, sdch, br");
            httpClient.DefaultRequestHeaders.AcceptLanguage.ParseAdd("zh-CN,zh;q=0.8");
            for (var i = 0; i < cookies.Count; i++)
            {
                var cookie = new Cookie(cookies[i].Name, cookies[i].Value, "/");
                handler.CookieContainer.Add(new Uri(TargetUrl), cookie); // Adding a Cookie
            }
            var byteArray = Encoding.ASCII.GetBytes("admin:test");
            httpClient.DefaultRequestHeaders.Authorization = new System.Net.Http.Headers.AuthenticationHeaderValue("Basic", Convert.ToBase64String(byteArray));
        }
    }
}