问题 如何使用HttpWebRequest在POST中转义URL编码数据

我正在尝试将URL编码的帖子发送到用PHP实现的REST API。 POST数据包含两个用户提供的字符串：

WebRequest request = HttpWebRequest.Create(new Uri(serverUri, "rest"));
request.Method = "POST";
request.ContentType = "application/x-www-form-urlencoded; charset=UTF-8";
request.Headers.Add("Content-Transfer-Encoding", "binary");

// Form the url-encoded credentials we'll use to log in
StringBuilder builder = new StringBuilder();
builder.Append("user=");
builder.Append(user);
builder.Append("&password=");
builder.Append(password);
byte[] credentials = Encoding.UTF8.GetBytes(builder.ToString());

// Write the url-encoded post data into the request stream.
request.ContentLength = credentials.Length;
using (Stream requestStream = request.GetRequestStream()) {
  requestStream.Write(credentials, 0, credentials.Length);
}

这会向包含的服务器发送HTTP请求 user=myusername&password=mypassword 在UTF-8中作为其POST数据。

如何逃避用户提供的字符串？ 例如，如果我有一个名为的用户 big&mean，如何对抗＆符号进行转义，以免它弄乱请求线？