.Net HttpClient不适用于cookie

Question

我正在尝试登录该网站并获取html正文。这是我的代码：

Dim cookies = New Net.CookieContainer
Dim handler = New Net.Http.HttpClientHandler
handler.UseCookies = True
handler.CookieContainer = cookies
Dim client = New Net.Http.HttpClient(handler)
Dim pairs = New List(Of KeyValuePair(Of String, String))
pairs.Add(New KeyValuePair(Of String, String)("doLogin", "1"))
pairs.Add(New KeyValuePair(Of String, String)("login", "admin"))
pairs.Add(New KeyValuePair(Of String, String)("password", "qwerty"))
Dim content = New Net.Http.FormUrlEncodedContent(pairs)
Dim request = New Net.Http.HttpRequestMessage
request.Method = Net.Http.HttpMethod.Post
request.RequestUri = New Uri("http://example.com")
request.Content = content
Dim response = client.SendAsync(request).Result
My.Computer.FileSystem.WriteAllText("C:/test.html", response.Content.ReadAsStringAsync.Result, False)

但是html页面说没有启用cookie：

  

找不到Cookie，请启用Cookie

我该怎么办？