Turn up logging to DEBUG.
If you are locked out of the CLI, do this:
# cd /opt/gluu/bin
# wget https://raw.githubusercontent.com/GluuFederation/community-edition-setup/master/static/scripts/setLogLevel.py
# wget https://raw.githubusercontent.com/GluuFederation/community-edition-setup/master/static/scripts/ldif.py
# chmod u+x setLogLevel.py
# ./setLogLevel.py -s oxauth -l DEBUG -F
And don't forget to set it back to `INFO` when you're done.
Also, under "Manage Authentication", you should point this at your AD server. See the [docs](https://gluu.org/docs/gluu-server/4.2/admin-guide/oxtrust-ui/#manage-ldap-authentication)