IOrganizationService _service;
OrganizationServiceProxy _serviceProxy;
ClientCredentials clientCredentials = new ClientCredentials();
//clientCredentials.UserName.UserName = ConfigurationManager.AppSettings["username"];
//clientCredentials.UserName.Password = ConfigurationManager.AppSettings["password"];
clientCredentials.Windows.ClientCredential = (NetworkCredential)CredentialCache.DefaultCredentials;
Uri organisationUri = new Uri(String.Format(ConfigurationManager.AppSettings["organisationUri"] + "XRMServices/2011/Organization.svc"));

ServicePointManager.ServerCertificateValidationCallback = AcceptAllCertificatePolicy;
IServiceConfiguration<IOrganizationService> serviceConfiguration = ServiceConfigurationFactory.CreateConfiguration<IOrganizationService>(organisationUri);
serviceConfiguration.Authenticate(clientCredentials);