Also, it's worth keeping in mind that TurnKey v15.x is based on Debian 9/Stretch (v14.x was based on 8/Jessie). Our OpenLDAP applaince has OpenLDAP (slapd) 2.4.44 installed from the Debian repos. So the Debian wiki pages may also be of assistance:
There is also the OpenLDAP 2.4 Admin guide, specifically the "Authentication Methods" section in the "Security Considerations" page which might also give you some pointers.
Good luck with it all, and please post back with anything of interest that you find.
By default, our OpenLDAP
By default, our OpenLDAP implmentation shoudl be somewhat locked down, but unfortunately, I'm no expert on OpenLDAP, so I can't directly help.
Having said that, a quick google turned up a couple of posts that may be relevant:
https://unix.stackexchange.com/questions/255061/enable-anonymous-bind-in-openldap
https://serverfault.com/questions/748758/enable-anonymous-bind-in-openldap/748904#748904
https://stackoverflow.com/questions/50497256/how-to-re-enable-anonymous-login-in-openldap
http://www.yolinux.com/TUTORIALS/LinuxTutorialLDAP-BindPW.html#LIMITANON
Also, it's worth keeping in mind that TurnKey v15.x is based on Debian 9/Stretch (v14.x was based on 8/Jessie). Our OpenLDAP applaince has OpenLDAP (slapd) 2.4.44 installed from the Debian repos. So the Debian wiki pages may also be of assistance:
https://wiki.debian.org/LDAP
There is also the OpenLDAP 2.4 Admin guide, specifically the "Authentication Methods" section in the "Security Considerations" page which might also give you some pointers.
Good luck with it all, and please post back with anything of interest that you find.