public function getAccessToken() 
    {
        $result = null;
        $options = $this->config->getAccessTokenConfiguration();
        $token = $this->getResponse('/oauth/token', $options);
        if (isset($token['access_token'])) {
            $this->config->setBearer($token['access_token']);
        }else {
            echo 'ERROR: no access token in API response';
        }
    }