private static JsonMetadataDocument GetMetadataDocument(string realm)
            {
                string acsMetadataEndpointUrlWithRealm = String.Format(CultureInfo.InvariantCulture, "{0}?realm={1}",
                                                                        GetAcsMetadataEndpointUrl(),
                                                                        realm);
                byte[] acsMetadata;
                using (WebClient webClient = new WebClient())
                {

                    acsMetadata = webClient.DownloadData(acsMetadataEndpointUrlWithRealm);
                }
                string jsonResponseString = Encoding.UTF8.GetString(acsMetadata);

                JavaScriptSerializer serializer = new JavaScriptSerializer();
                JsonMetadataDocument document = serializer.Deserialize<JsonMetadataDocument>(jsonResponseString);

                if (null == document)
                {
                    throw new Exception("No metadata document found at the global endpoint " + acsMetadataEndpointUrlWithRealm);
                }

                return document;
            }