[求助] Go 爬虫无法获取北邮人论坛 cookie 的疑惑

背景

这两天尝试写个 Go 爬虫爬北邮人论坛，期望能登录后保存 cookie，后续的访问都带着这个 cookie。查看资料推荐用net/http/cookiejar。
目前能登录成功，获取成功登录 Json。但是发现并未获取登录后的 cookie，导致后续直接 Get 帖子正文报错**“您未登录,请登录后继续操作”**
请教各位大大，这种情况哪里出错了？

实现

package main

import (
  "net/http/cookiejar"
  "net/url"
  "strings"
  "fmt"
  "net/http"
  "crypto/tls"
  "io/ioutil"
)

func main() {
  // init cookiejar
  var cookieJar *cookiejar.Jar
  cookieJar, _ = cookiejar.New(nil)

  // init client with cookiejar
  httpClient := &http.Client{
    Jar: cookieJar,
  }

  // login param
  postValues := url.Values{}
  postValues.Set("id", "ID")
  postValues.Set("passwd", "PWD")
  postValues.Set("s-mode", "0")
  postValues.Set("CookieDate", "3")

  // request for login
  httpReq, _ := http.NewRequest("POST", "https://bbs.byr.cn/user/ajax_login.json", strings.NewReader(postValues.Encode()))
  httpReq.Header.Set("Content-Type", "application/x-www-form-urlencoded; param=value")
  httpReq.Header.Add("X-Requested-With", "XMLHttpRequest")
  httpReq.Header.Add("Connection", "keep-alive")
  httpReq.Header.Add("User-Agent", "Mozilla/5.0")
  httpReq.Header.Add("Referer", "https://bbs.byr.cn")
  httpReq.Header.Add("Accept", "application/json, text/javascript, */*; q=0.01")
  httpReq.Header.Add("authority", "bbs.byr.cn")
  // for nginx/1.10
  httpClient.Transport = &http.Transport{
    TLSNextProto: make(map[string]func(authority string, c *tls.Conn) http.RoundTripper),
  }

  // login
  httpResp, _ := httpClient.Do( httpReq)
  fmt.Printf("req cookies: %s \n", httpReq.Cookies())
  fmt.Printf("resp cookies: %s \n", httpResp.Cookies())

  // request to get article content
  httpReq1, _ := http.NewRequest("GET", "https://bbs.byr.cn/article/Golang/842", nil)
  httpReq1.Header.Add("X-Requested-With", "XMLHttpRequest")
  httpResp1, _ := httpClient.Do( httpReq1)
  body, _ := ioutil.ReadAll( httpResp1.Body)
  fmt.Println(string(body))
}

输出(可见 cookie 为空)：

req cookies: [] 
resp cookies: [] 
(...省略...)
<h5>产生错误的可能原因：</h5><ul><li><samp class="ico-pos-dot"></samp>您未登录,请登录后继续操作</li>
(...省略...)

困扰多时，求各位指点