This post will run through Installing LDAP on Ubuntu 18.04. Allowing you to authenticate users via LDAP. As well as setting up thier Linux groups. You will need a server or desktop install to begin with. Lightweight Directory Access Protocol (LDAP) is a network protocol for accessing and manipulating information stored in a directory.
This HOWTO also works on a Raspberry PI 3 running the Ubuntu MATE image!
While sorting out this HOWTO and learning how to setup Zentyal I used my Network lab, See how to set up your own. If you do use this then remember to turn of the DHCP server in the router if you intend to use the DHCP server within the Zentyal server.