public static function buildObtainTokenUrl($client_id, $redirect_uri,
        $scope) {
        $params = sprintf(
            "client_id=%s&response_type=%s&redirect_uri=%s&scope=%s",
            $client_id, "code", $redirect_uri, implode(" ", $scope)
            );
        return sprintf("%s/oauth/authorize?%s", Config::$MONEY_URL, $params);
    }