In sssd, simple access_provider is not working as expected

Issue

• Even after allowing only single user in sssd.conf file, ALL users are able to login. /var/log/secure logs show:

Mar 11 13:09:31 test7-rh sshd[4179]: pam_succeed_if(sshd:auth): no condition detected; module succeeded  <--------
Mar 11 13:09:32 test7-rh sshd[4179]: pam_sss(sshd:auth): authentication success; logname= uid=0 euid=0 tty=ssh ruser= rhost=137.45.0.23 user=ad_user2
Mar 11 13:09:32 test7-rh sshd[4179]: pam_succeed_if(sshd:account): no condition detected; module succeeded  <-------
Mar 11 13:09:32 test7-rh sshd[4179]: Accepted password for jdalton3 from 137.45.0.23 port 52080 ssh2
Mar 11 13:09:32 test7-rh sshd[4179]: pam_unix(sshd:session): session opened for user ad_user2 by (uid=0)
Mar 11 13:10:15 test7-rh sshd[4179]: pam_unix(sshd:session): session closed for user ad_user2

• sssd.conf not honouring access settings from configuration:

access_provider = simple
simple_allow_users = ad_user1

Still all AD users are able to login(ideally on ad_user1 should be able to login)