通过HttpWebRequest上的边界完成字段

我正试图通过C#应用程序的HttpWebRequest登录到一个网站。登录页面的帖子数据看起来像：

-----------------------------18327245165630'r'n
Content-Disposition: form-data; name="user"'r'n
'r'n
123'r'n
-----------------------------18327245165630'r'n
Content-Disposition: form-data; name="pass"'r'n
'r'n
1234'r'n
-----------------------------18327245165630'r'n
Content-Disposition: form-data; name="mode"'r'n
'r'n
login'r'n
-----------------------------18327245165630'r'n
Content-Disposition: form-data; name="submit"'r'n
'r'n
Submit'r'n
-----------------------------18327245165630--'r'n

字段为user和pass，在浏览器上完成的值为123以及1234。

问题是如何通过HttpWebRequest发送这些值？

我的代码看起来像：

private void loginButton_Click(object sender, EventArgs e)
{
    try
    {
        HttpWebRequest oRequest = null;
        oRequest = (HttpWebRequest)HttpWebRequest.Create(loginLinkPost);
        oRequest.ContentType = "multipart/form-data; boundary=" + PostData.boundary;
        oRequest.UserAgent = "Mozilla/5.0 (Windows NT 6.3; WOW64; rv:28.0) Gecko/20100101 Firefox/28.0";
        oRequest.KeepAlive = true;
        oRequest.AllowAutoRedirect = true;
        oRequest.Method = "POST";
        oRequest.CookieContainer = cookies;
        PostData pData = new PostData();
        Encoding encoding = Encoding.UTF8;
        System.IO.Stream oStream = null;
        pData.Params.Add(new PostDataParam("email", this.usernameBox.Text, PostDataParamType.Field));
        pData.Params.Add(new PostDataParam("password", this.passwordBox.Text, PostDataParamType.Field));
        pData.Params.Add(new PostDataParam("mode", "login", PostDataParamType.Field));
        pData.Params.Add(new PostDataParam("submit", "Submit", PostDataParamType.Field));
        byte[] buffer = encoding.GetBytes(pData.GetPostData());
        oRequest.ContentLength = buffer.Length;
        oStream = oRequest.GetRequestStream();
        oStream.Write(buffer, 0, buffer.Length);
        oStream.Close();
        string sursa = "";
        using (HttpWebResponse oResponse = (HttpWebResponse)oRequest.GetResponse())
        {
            if (oResponse.StatusCode == HttpStatusCode.OK)
            {
                System.IO.Stream responseStream = oResponse.GetResponseStream();
                System.IO.StreamReader reader = new System.IO.StreamReader(responseStream, Encoding.UTF8);
                sursa = reader.ReadToEnd();
                MessageBox.Show("Logged in :)!");
            }
            else
            {
                setStatus("Server response failed...");
                MessageBox.Show("Server failed to respond!", "Error!");
                setStatus("Ready...");
            }
        }
    }
    catch(Exception ex)
    {
        setStatus("Error while trying to log in...");
        MessageBox.Show(ex.ToString(), "Error when try to login...");
        setStatus("Ready...");
    } 
}

PostData.cs类：

namespace IPSocksBot
{
    public class PostData
    {
        public static string boundary = "---------------------------" + DateTime.Now.Ticks.ToString("x");
        private List<PostDataParam> m_Params;
        public List<PostDataParam> Params
        {
            get { return m_Params; }
            set { m_Params = value; }
        }
        public PostData()
        {
            m_Params = new List<PostDataParam>();
        }
        public string GetPostData()
        {
            StringBuilder sb = new StringBuilder();
            foreach (PostDataParam p in m_Params)
            {
                sb.AppendLine("--" + boundary + "''r''n");
                if (p.Type == PostDataParamType.File)
                {
                    sb.AppendLine(string.Format("Content-Disposition: file; name='"{0}'"; filename='"{1}'"", p.Name, p.FileName));
                    sb.AppendLine("Content-Type: application/octet-stream");
                    sb.AppendLine();
                    sb.AppendLine(p.Value);
                }
                else
                {
                    sb.AppendLine(string.Format("Content-Disposition: form-data; name='"{0}'"''r''n", p.Name));
                    sb.AppendLine("''r''n");
                    sb.AppendLine(p.Value + "''r''n");
                }
            }
            sb.AppendLine("--" +boundary + "--" + "''r''n");
            return sb.ToString();
        }
    }
    public enum PostDataParamType
    {
        Field,
        File
    }
    public class PostDataParam
    {
        public PostDataParam(string name, string value, PostDataParamType type)
        {
            Name = name;
            Value = value;
            Type = type;
        }
        public PostDataParam(string name, string filename, string value, PostDataParamType type)
        {
            Name = name;
            Value = value;
            FileName = filename;
            Type = type;
        }
        public string Name;
        public string FileName;
        public string Value;
        public PostDataParamType Type;
    }
}

我缺少什么？为什么我的价值观没有提交？我用Fiddler来查看我的发送帖子值，它们完全相同。

-----------------------------18327245165630'r'n
Content-Disposition: form-data; name="user"'r'n
'r'n
123'r'n

pData.Params.Add(new PostDataParam("user", this.usernameBox.Text, PostDataParamType.Field));
pData.Params.Add(new PostDataParam("pass", this.passwordBox.Text, PostDataParamType.Field));
pData.Params.Add(new PostDataParam("mode", "login", PostDataParamType.Field));
pData.Params.Add(new PostDataParam("submit", "Submit", PostDataParamType.Field));