Only the auth service is supported.
In the case of the su(1) application the historical usage is to permit the superuser to adopt the identity of a lesser user without the use of a password. To obtain this behavior with PAM the following pair of lines are needed for the corresponding entry in the /etc/pam.d/su configuration file:
# su authentication. Root is granted access by default. auth sufficient pam_rootok.so auth required pam_unix.so
su(1), pam.conf(5), pam.d(5), pam(7)
pam_rootok was written by Andrew G. Morgan, <email@example.com>.