I understand that this request is not easy to implement, BUT...
It is in my opinion the ONLY right way for us to go.
Many people use DataBases (DB) to handle authentication because it is an easy way to do it. It was never designed to do this and will eventually cause problems later on down the road. Lightweight Directory Access Protocol (LDAP) can be difficult to set up correctly and there are too many different ways to do it.
The good thing about this is that we would not have to start from nothing.
I hesitate to suggest this, BUT the easy way to do this would be to integrate Zimbra with ISPConfig. Zimbra is a HEAVY duty mail server that comes with LDAP, MySQL, Tomcat, Ajax, Java & etc. implementations. There would be no need to learn and implement a new LDAP system that integrates with mail system that use MySQL.
In my opinion (+10 years in business) this is the best way to significantly improve ISPConfig while keeping the load on the good people who code this software to minimum.
I look forward to your opinions on the matter.
I belive we all need this one.