The use of Zend http client by itself is better than using the curl adapter.Besides the username and password are not required to authenticate. You can perform the operation only after you have received th access token from the authorization procedure of Oauth2 of Box-API. The zend http client call that can be used is the following:
$client = new Zend_Http_Client('https://api.box.com/2.0/folders/0');
$client->setMethod(Zend_Http_Client::GET);
$client->setHeaders('Authorization: Bearer '.$access_token);
$response = $client->request()->getBody();
My 2 cents.