You will need to develop your own Directory Manager Plugin that will be able interpret your custom tables so that Joget can access them programmatically.
The documentation suggests that there are 3 built-in Directory Managers: LDAP Directory Manager Security Enhanced Directory Manager Sync LDAP User Directory Manager
These options do not show up for me.
Joel
I believe they are in the enterprise edition. Try to re-install your Joget by replacing it with the enterprise war file or run through the bundle installer of enterprise.