I have to agree with Peter, @yammy. Hiding the password, in this scenario, does nothing to improve your security. In fact, it lulls you into a false sense of security which is worse.
The author of this plugin already explained his position on why the password is in cleartext, and IMHO he's 100% correct: https://wordpress.org/support/topic/works-as-it-should?replies=3#post-3918398
Offline-authentication was never meant for use on shared, multi-user systems.