I need to know and receive any documentation or advice if there is an experience how to apply the ldap plug in of Jive with a propietary system which is working without any Ldap or single sign on solution.
Or any kind of suggestion? Since the client decided to not work with this kind of solutions.
I would either instrument and ldap interface on the legacy system ( could be costly) or build an SSO adapter to whatever paradigms your custom system uses. Spring security is pretty robust, but if there is a way you can go with an ootb authprovider, such as saml2, kerberos5, or even ldap you'll be in a better place.
As a rule of thumb, I try to silo off non standard interfaces behavior and not let its "specialness" permeate too far into the more standard system.