Login (XML)

 contentType = "text/xml";//or application/xml
                postData = "" + accountID + "" + password + "";
                responseString = CallService(url, postData, contentType);

                //Parse login result
                byte[] bytes = System.Text.Encoding.UTF8.GetBytes(responseString);
                MemoryStream ms = new MemoryStream(bytes);
                XmlReader reader = XmlReader.Create(ms);
                reader.MoveToContent();

                string status = null;
                string key = null;
                while (reader.Read())
                {
                    if (reader.NodeType == XmlNodeType.Element)
                    {
                        if (reader.Name == "Status")
                        {
                            while (reader.Read())
                            {
                                if (reader.NodeType == XmlNodeType.Text)
                                {
                                    status = reader.Value;
                                }
                                else if (reader.NodeType == XmlNodeType.EndElement && reader.Name == "Status")
                                {
                                    break;
                                }
                            }
                        }
                        else if (reader.Name == "Key")
                        {
                            while (reader.Read())
                            {
                                if (reader.NodeType == XmlNodeType.Text)
                                {
                                    key = reader.Value;
                                }
                                else if (reader.NodeType == XmlNodeType.EndElement && reader.Name == "Key")
                                {
                                    break;
                                }
                            }
                        }
                    }
                }

                if (status == "Success")
                {
                    this.key = key;
                }
            }

            txtResult.Text += responseString;