vCAC plug-in, unable to register a new vCAC host over https

Has anyone had any luck registering a vCAC server over https with the vCAC plug-in for vCO?  Seems to work fine for me over http, but the "Manage SSL certificates" workflow (called from "Add a vCAC host" workflow) isn't able to validate an https URL, throwing the below exception:

org/apache/commons/validator/UrlValidator (Workflow:Manage SSL certificates / Get URL certificates (item0)#6)

I've tried adding the vCAC cert to vCO and restarting vCO prior to running the workflow.  Also, the certificate CN matches the host fqdn of the URL.

Thanks,

David