Which of the following PAM modules allows the system administrator to use an arbitrary file...

 The pam_listfile module is a PAM module that allows the system administrator to use an arbitrary file containing a list of user and group names with restrictions on the system resources available to them. The module can be used to deny or allow access to services based on the contents of the file. The file can contain items such as usernames, group names, terminal names, remote host names, remote user names, or shell names. The module can be configured to match the item against the file and take the appropriate action, such as allowing or denying access, or ignoring the request. The module can also be restricted to apply only to a specific user or group class. The file should be a plain text file with one item per line and not be world writable12.

References:

pam_listfile(8) - Linux man page: A manual page for the pam_listfile module, which explains its syntax, options, and examples.

pam_listfile(8) - Linux manual page - man7.org: Another manual page for the pam_listfile module, which provides similar information as the previous reference.