Check if PAM is throwing any issues:
tail -f /var/log/secure
authentication should be successful = your PAM integration/authentication works
Access denied = You authentication successfull but dont have the necessary access rights.
Check the authentication module configuration:
i.e. /etc/sssd/sssd.conf
authentication module logs:
i.e. /var/log/sssd/*.log
Check permissions to service config file. should be 660. I.e.:
chmod mariadb:mariadb /etc/pam.d/MariaDB
http://dbversity.com/configuring-mariadb-with-pamkerberos/
Make sure the correct PAM modules are installed (you never know...)
Check of group policies (ad_gpo_access_control) are to be set or not (/var/log/sssd/*.log) and man sssd-ad