Intranet with no public logins

[fulv]

Specific use case question: I'm working on an intranet, which by definition should only allow approved user to log in. Is it possible to do this?

Since there already are user accounts registered locally in Plone (before installing this plugin), I was thinking that if we could add the external identities to the local accounts using authomatic-handler, then we could limit which external identities will be allowed to log in. Is this doable, and if so, how?