It depends on your user referential.
You need to be able to connect your login java module with that base. it is is LDAP, you might consider framework like OpenLDAP.
Plus you have to consider what is include in your "login" perimeter: It is is an "habilitation" login process, you need to have more that just the user name, but also other parameters helping your java module to grant him access (its group, which might be in LDAP, but also the kind of action he wants to make, in order to check if he has the required accreditation level)