[Dovecot] where is "pam_listfile.so" for static userdb?

[OpenMacNews]

hi all,

i'm setting up Dovecot on OSX to use PAM authentication against a 
flat_file/static userdb (tho i will _eventually_ mv to pgsql ...).

iiuc, to do so i need something like:

===================================
(EDITOR) /etc/pam.d/dovecot.imap
auth required pam_listfile.so item=user sense=allow file=/var/dovecot/imapusers 
onerr=fail
===================================

for a userdb listing in "/var/imapuser".

all simple & good, except --
      -- where's "pam_listfile.so" on OSX?

% ls /usr/lib/pam/
    pam_afpmount.so  pam_nologin.so  pam_securetty.so       pam_uwtmp.so
    pam_deny.so      pam_permit.so   pam_securityserver.so  pam_wheel.so
    pam_netinfo.so   pam_rootok.so   pam_unix.so

do i have to grab-n-install it from somewhere? or are one of these ^ an 
'equivalent' ...

this _should_ be simple :-}

thanks,

richard