vsftpd pam problem

[Terry]

Hi going by the docs for virtual users i have got to this file vsftpd.pam

auth required /lib/security/pam_userdb.so db=/etc/vsftpd_login
account required /lib/security/pam_userdb.so db=/etc/vsftpd_login

 From google i gather pam_userdb.so isn't part of OpenPAM which is what 
FreeBSD uses. So how do Freebsd users get round it or am i missing some 
thing really silly.

Thanks