The straight forward answer is no. The CA server is not meant for authentication. However it does check the password for the first enrollment, so if you never stored the crypto and set enrollment attempts to unlimited it would validate against the static (unchangeable) password set during registration. Probably not the best idea but might be fine for some use case.
I did an implementation storing users and passwords in the blockchain, checked on every web app login, with update rights only for the user. If you want passwords changeable, you have to store them somewhere the user can get to them. LDAP (recommended), database, file system, blockchain, somewhere.
Users belong to an Org. So if a peer and the user are in an Org that has access to multiple channels, all is well.