// For external domain.
        public static IActiveDirectory GetActiveDirectoryInterface(string connectionString)
        {
            if (ADImplementation == null)
            {
                ADImplementation = new ActiveDirectoryImplementation(connectionString);
            }

            return(ADImplementation);
        }
        public static IActiveDirectory GetActiveDirectoryInterface()
        {
            if (ADImplementation == null)
            {
                ADImplementation = new ActiveDirectoryImplementation();
            }

            return(ADImplementation);
        }