Salesforce OAuth Refresh

/// <summary>
/// Refresh the current Salesforce access token
/// </summary>
/// <param name="token">
/// The refresh token provided by Salesforce's OAuth Server on initial login
/// </param>
/// <returns>
/// Access token, endpoint URL and other nice things.
/// </returns>
/// <exception cref="ConnectionException"></exception>
/// <exception cref="ArguementException"></exception>
public static SessionInfo RefreshToken(string clientId, string token)
{
    if (string.IsNullOrEmpty(clientId) || string.IsNullOrEmpty(token)) { throw new ArgumentException("clientId and token are required"); }

    string postData = string.Format("grant_type=refresh_token&client_id={0}&refresh_token={1}", clientId, token);
    byte[] data = Encoding.UTF8.GetBytes(postData);

    HttpWebRequest request = (HttpWebRequest)WebRequest.Create(Config.RefreshTokenUri);
    request.Method = "POST";
    request.ContentType = "application/x-www-form-urlencoded";
    request.Accept = "application/json";
    request.ContentLength = data.Length;

    using (Stream requestStream = request.GetRequestStream())
    {
        requestStream.Write(data, 0, data.Length);
    }

    WebResponse response = null;
    SessionInfo authResponse = null;

    try
    {
        response = request.GetResponse();
        string authResponseJson = new StreamReader(response.GetResponseStream()).ReadToEnd();
        authResponse = JsonConvert.DeserializeObject<SessionInfo>(authResponseJson);
    }
    catch (WebException ex)
    {
        string errorJson = new StreamReader(ex.Response.GetResponseStream()).ReadToEnd();
        ex.Response.GetResponseStream().Close();
        ex.Response.Close();
        SessionError error = JsonConvert.DeserializeObject<SessionError>(errorJson);
        throw new ConnectionException(error);
    }
    catch (JsonSerializationException ex)
    {
        System.Diagnostics.Trace.Assert(false, ex.Message); // Not too interested in this
    }
    catch (JsonReaderException ex)
    {
        System.Diagnostics.Trace.Assert(false, ex.Message); // Ditto
    }
    finally
    {
        response.GetResponseStream().Close();
        response.Close();
    }

    return authResponse;
}