WEB项目后端跨域请求

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Net;
using System.Text;
using System.Web;
using System.Web.SessionState;

namespace GL
{
    public class CrossDomainHandler:IHttpModule, IRequiresSessionState
    {
        /// <summary>
        /// 释放内存
        /// </summary>
        public void Dispose()
        {
        }

        /// <summary>
        /// 开始请求
        /// </summary>
        /// <param name="context"></param>
        public void Init(HttpApplication context)
        {
            //页面开始请求时，绑定时间
            context.BeginRequest += new EventHandler(context_PreRequestHandlerExecute);
        }

        /// <summary>
        /// 请求处理
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        void context_PreRequestHandlerExecute(object sender, EventArgs e)
        {

            HttpApplication app = (HttpApplication)sender;
            HttpContext context = app.Context;

            context.Response.AppendHeader("charset", "utf-8");
            context.Response.AppendHeader("defaultCharset", "utf-8");
            context.Response.AppendHeader("Content-Type", "text/html; charset=utf-8");

            var relativeAddr = context.Request.AppRelativeCurrentExecutionFilePath.Remove(0, 2);
            if (relativeAddr.StartsWith("Server")) 
            {
                var url = string.Concat("http://localhost:89", relativeAddr.Substring(relativeAddr.IndexOf('/')));
                HttpWebRequest request = WebRequest.Create(url) as HttpWebRequest;
                request.Method = "POST";
                request.ContentType = "application/x-www-form-urlencoded";
                var rs = request.GetRequestStream();
                var sb = new StringBuilder("a=a&");
                context.Request.Form.AllKeys.ToList().ForEach(name =>
                {
                    sb.AppendFormat("{0}={1}&", name, context.Request.Form[name]);
                });
                var str = sb.ToString();
                if(str.Contains('&'))
                {
                    str = str.Substring(0, str.Length - 1);
                }
                var sw = new StreamWriter(rs, Encoding.UTF8);
                sw.Write(sb.ToString());
                sw.Close();

                request.Timeout = 60 * 1000;
                var response = request.GetResponse() as HttpWebResponse;
                var ps = response.GetResponseStream();
                var reader = new StreamReader(ps, Encoding.UTF8);
                string html = reader.ReadToEnd();
                ps.Close();
                context.Response.Write(html);
                context.Response.End();
            }
        }
    }
}