public function clientCredentials($scope = 'public')
    {
        if (is_array($scope)) {
            $scope = implode(' ', $scope);
        }

        $token_response = $this->request(self::CLIENT_CREDENTIALS_TOKEN_ENDPOINT, array(
            'grant_type' => 'client_credentials',
            'scope' => $scope
        ), "POST", false);

        return $token_response;
    }