How to escape URL-encoded data in POST with HttpWebRequest

I am trying to send an URL-encoded post to a REST API implemented in PHP. The POST data contains two user-provided strings:

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();
开发者_如何学编程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);
}

This sends a HTTP request to the server containing user=myusername&password=mypassword in UTF-8 as its POST data.

How can I escape the user-provided strings? For example, if I had a user named big&mean, how should the ampersand be escaped so that it does not mess up the request line?

---

You can use the static HttpUtility class in System.Web for encoding and decoding HTML and Url related values.

Try HttpUtility.UrlEncode().

---

It would seem that System.Web is obsolete - the newer way to access it is System.Net.WebUtility.HtmlEncode