Reliable use of System Name? Multi-file passwords

How can I ensure that the FMP user name is set to the system name and not a custom name?

I think I can get by with just three passwords:

Me - master password

Edit - people who need to edit the data

View - people who need to see, but not edit

as long as I can ensure that users can't fake their user name.

(I will keep an audit log of every change and who make it, preventing

anyone from being "bad' without getting "caught".)

We are running OS X, so users must be authenticated to even use

the computers. Thus, I *think* if I can restrict it to the system name,

that I am safe. True?

I have one user who wants to connect from a PC. What would I have

to do in that case? Can I detect that its a connection via a PC?

ALTERNATIVELY, does FMP Server have a way of efficiently managing

lots of user passwords that should be the same for numerous files?

What's the right way to do this?

(Yes, I did RTFM... TFM doesn't discuss it... or if it does, I need

help finding it... I only find discussion of single-file and brief

mention of multi-file case... and no details at all on using system

name with reliability.)

Thanks!