private $config;
        private static $instance;

        private static function getInstance() {
            if(is_null(self::$instance)){
                self::$instance = new DSConfig();
            }

            return self::$instance;
        }

        public function __construct() {
            date_default_timezone_set('UTC');

            $clientId = getenv("DS_CLIENT_ID");
            if (!is_null($clientId) and !empty($clientId)) {
                $this->config["DS_CLIENT_ID"] = $clientId;
                $this->config["DS_AUTH_SERVER"] = getenv("DS_AUTH_SERVER");
                $this->config["DS_IMPERSONATED_USER_GUID"] = getenv("DS_IMPERSONATED_USER_GUID");
                $this->config["DS_TARGET_ACCOUNT_ID"] = getenv("DS_TARGET_ACCOUNT_ID");
                $this->config["SIGNER_EMAIL"] = getenv("SIGNER_EMAIL");
                $this->config["SIGNER_NAME"] = getenv("SIGNER_NAME");
                $this->config["CC_EMAIL"] = getenv("CC_EMAIL");
                $this->config["CC_NAME"] = getenv("CC_NAME");
                $this->config["DS_PRIVATE_KEY"] = getenv("DS_PRIVATE_KEY");
            } else {
                $this->config = parse_ini_file('ds_config.ini', true);
            }
        }

        private function _auth_server() {
            return $this->config["DS_AUTH_SERVER"];
        }
        public static  function auth_server() {
            return self::getInstance()->_auth_server();
        }
        private function _client_id() {
            return $this->config["DS_CLIENT_ID"];
        }
        public static  function client_id() {
            return self::getInstance()->_client_id();
        }
        private function _impersonated_user_guid() {
            return $this->config["DS_IMPERSONATED_USER_GUID"];
        }
        public static  function impersonated_user_guid() {
            return self::getInstance()->_impersonated_user_guid();
        }
        private function _target_account_id() {
            return $this->config["DS_TARGET_ACCOUNT_ID"];
        }
        public static  function target_account_id(){
            return self::getInstance()->_target_account_id();
        }
        private function _signer_email() {
            return $this->config["SIGNER_EMAIL"];
        }
        public static  function signer_email(){
            return self::getInstance()->_signer_email();
        }
        private function _signer_name(){
            return $this->config["SIGNER_NAME"];
        }
        public static  function signer_name(){
            return self::getInstance()->_signer_name();
        }
        private function _cc_email() {
            return $this->config["CC_EMAIL"];
        }
        public static function cc_email(){
            return self::getInstance()->_cc_email();
        }
        private function _cc_name(){
            return $this->config["CC_NAME"];
        }
        public static function cc_name(){
            return self::getInstance()->_cc_name();
        }
        private function _private_key() {
            return $this->config["DS_PRIVATE_KEY"];
        }
        public static function private_key(){
            return self::getInstance()->_private_key();
        }
        public static function aud() {
            $auth_server = self::getInstance()->_auth_server();

            if (strpos($auth_server, 'https://') !== false) {
                $aud = substr($auth_server, 8);
            } else { # assuming http://blah
                $aud = substr($auth_server, 7);
            }
            return $aud;
        }
        public static function api() {
            return "restapi/v2";
        }
        public static function jwt_scope() {
             return "signature";
        }