The documentation states
To list CDN-only containers, follow the same operation for Storage which lists all containers. The only difference is which service object you execute the method on.
But what is the right service object. I tried:
$service = objectStoreService('cloudFiles', $region);
$service = objectStoreCDNService('cloudFilesCDN', $region);
$service = objectStoreCDNService('cloudFiles', $region);
$service = objectStoreService('cloudFilesCDN', $region);
And $containers = $service->listContainers()
or $containers->listContainers(array('enabled_only' => TRUE))
with all of the above to no avail.