No one has mentioned the super-handy SESSION yet. SESSION allows you to define and manage LDEV sessions from a existing CMS logon (if on the same system). I don't think it would be terrifically hard to add the ability to read the session authentication details from a file to SESSION.
This is not very much different of what one would get by using a SNA multi-session product like supersession. If I remember, Computer Associates used to have a product called V-Term doing something similar. If you're willing to spend money, PVM is very cheap. Several people have already commented on it. If you're going to store PWs in a file, SFS is probably a slightly (note: *slightly*) safer option. Gives you a bit more granular access control.
