使用代码访问http资源，我们通常用WebRequest，当然，HttpClient提供了更方便的封装，我用得更多。只是碰到一些需要(cookie)鉴权的情况，需要把cookie伴随请求一起发到服务器，如下：

var m = new HttpClient();var url = new Uri("http://localhost:4567/test");var cookie = "mycookie=valueofcookie; expires=Thu, 14-Nov-2013 07:21:28 GMT; path=/; HttpOnly";

1，使用WebRequest，完全没问题：

var req = (HttpWebRequest)WebRequest.Create(url);req.Method = "POST";req.ContentLength = 0;req.Headers.Add("Cookie", cookie);var res = (HttpWebResponse)req.GetResponse();using (var stream = res.GetResponseStream()){    if (stream != null) Console.WriteLine(new StreamReader(stream, System.Text.Encoding.UTF8).ReadToEnd());}

2，如果要用HttpClient的话呢？我失败了两次：

我想这么写（2.1）：

m.DefaultRequestHeaders.Add("Cookie", cookie);var t = await m.PostAsync(url, null);var c = await t.Content.ReadAsStringAsync();Console.WriteLine(c);

失败，于是这么写（2.2）

var req = new HttpRequestMessage(HttpMethod.Post, url);req.Headers.Add("Cookie", cookie);var t = await m.SendAsync(req);var c = await t.Content.ReadAsStringAsync();Console.WriteLine(c);

仍然失败，查到 ，有结论了，使用CookieContainer

var baseAddress = new Uri("http://example.com");var cookieContainer = new CookieContainer();using (var handler = new HttpClientHandler() { CookieContainer = cookieContainer })using (var client = new HttpClient(handler) { BaseAddress = baseAddress }){    //此处是顺便演示如何传Post参数    var content = new FormUrlEncodedContent(new[]    {        new KeyValuePair
     
      ("foo", "bar"),        new KeyValuePair
      
       ("baz", "bazinga"),    });    cookieContainer.Add(baseAddress, new Cookie("CookieName", "cookie_value"));    var result = client.PostAsync("/test", content).Result;    result.EnsureSuccessStatusCode();}
      
     

此时有人提出，其实2.2的写法是可以的，之所以cookie没有传递到过去，是因为HttpClientHandler默认用了CookieContainer，所以会忽略掉Header里面的Cookie设置，因此你要做的就是把CookieContainer从HttpClientHandler里禁掉，测试通过：

var m = new HttpClient(new HttpClientHandler { UseCookies = false });

此时方法2.2一个字不要动，cookie顺利传递