将PHP cURL转换为C＃WebClient

Question

I am trying to convert a piece of PHP cURL code to C# using the WebClient but I can't figure out how to implement the CurlFile parameter from the array.

Here is the original PHP code:

$post_data = array('password'=>'pswd',
                   'username'=>'usr',
                   'textfile'=>new CURLFile('C:\data_stats.txt'),
                  );

$curl_obj = curl_init('https://www.website.com');
curl_setopt($curl_obj, CURLOPT_POST, true);
curl_setopt($curl_obj, CURLOPT_POSTFIELDS, $post_data);
$data = curl_exec($curl_obj);

And there is the C# code I came up with (I managed to send the password and username parameters but I don't know how to send the file with the key 'textfile' along with those parameters)

        using (var client = new WebClient())
        {
            var post_data = new NameValueCollection();
            post_data["password"] = "pswd";
            post_data["username"] = "usr";

            var response = client.UploadValues("www.website.com", post_data);

        }