Most of the OS's currently on the market can use a single sign-on capability with Kerberos or something similar to that. Using a single sign-on functionality is convenient to the user as well as reducing the systems administration tasks involved with create/modifying/deleting users.
This is complicated by the fact that some parts of the country would routinely set up Unix users with names like 'user12' for the person who logs into the app as '12'. The passwords for these things are, of course, set in different ways, and managed in different places. It's possible for our app to have a custom menu option that calls passwd to set the Unix password for a user; it's important that the person understand this distinction. (The actual passwd binary probably was originally written as a gnu drop-in replacement for the SysV passwd.)