the the java script could save inside a txt or a raw file(text inside) with the login suplied and the time it has benn loged you could look at the time and the ip of that access in the hfs log...
javascript is client side, it can't access HFS log.
anyway, HFS 2.0 accept any inexistant username, with any password.
and that username in the logs, appears, so i think this is the solution for you.
this thing should not work in 2.1, be warned.