The authentication process would occur in the terminal server via propietary protocols (e.g. ERPCD on annexes), or industry standard protocols like TACACS or RADIUS protocols. This authentication would have nothing to do with unix user ids, so there would be no crunch on allocation of user ids.
Read-only access to menus and news would not require any authentication at all, and rfc1413 (ident) between server and terminal server could provide write/send/post access to things. Otherwise, one would have to enter passwords whenever fetching new email or making postings.