A maintainers question: how to create a user?

[Aryeh Friedman]

See subject for the main question... the details: I am the maintainer of
devel/aegis and the final installation step typically (linux RPM's for
example) is to create a user to hold the baselines (in svn/cvs/csup speak
the project's repo) of the varioous projects managed by aegis... customerly
this is MUST be a non-logginable (you MUST [requirements document meaning
of upper case MUST/SHOULD/MAY {NOT}) but allow for su from either root or
via sudo a member of "wheel")... it is a standard account in all other
respects for example I typically set it to tcsh but the port might want to
make that an make time option... what is the best way of setting this all
up (both the no options and the options based versions)