To restrict users from accessing the system using Centrify free can be easily managed by using the following files

/etc/centrifydc/users.allow
/etc/centrifydc/groups.allow
/etc/centrifydc/users.deny
/etc/centrifydc/groups.deny

1. You have to manually create the the files accordingly and place it at /etc/centifydc. Next you have to  line 273 and uncomment the line

.....
pam.allow.users: file:/etc/centrifydc/users.allow
.....

If you are blocking by groups, you can likewise uncomment the

.....
pam.allow.groups: file:/etc/centrifydc/groups.allow
.....

2. Flush and Reload Centrify-Free

# adflush
# adreload

3. Add users you wish to have access into the system into /etc/centrifydc/users.allow