I want to log in into a website using C# code.

Here's the html code of the example form:

<form action="http://www.site.com/login.php" method="post" name="login" id="login">
<table border="0" cellpadding="2" cellspacing="0">
<tbody>
<tr><td><b>User:</b></td><td colspan=\"2\"><b>Password:</b></td></tr>
<tr>
<td><input class="inputbg" name="user" type="text"></td>
<td><input class="inputbg" name="password" type="password"></td>
<td><input type="submit" name="user_control" value="Submit" class="buttonbg"></td>
</tr>
</tbody></table>
</form>

This is what I have tried so far with unsuccessful results:

HttpWebRequest request = (HttpWebRequest)WebRequest.Create("http://www.site.com/login.php");
request.Method = "POST";
using (StreamWriter writer = new StreamWriter(request.GetRequestStream(), Encoding.ASCII))
{
    writer.Write("user=user&password=pass&user_control=Eingabe");
}

HttpWebResponse response = (HttpWebResponse)request.GetResponse();

using (StreamReader reader = new StreamReader(response.GetResponseStream()))
{
    stream = new StreamWriter("login.html");
    stream.Write(reader.ReadToEnd());
    stream.Close();
}

Any Ideas, why this is failing?