Thanks Tom,
I was looking at IdentitySession together with User, Group, UserQuery and GroupQuery interfaces. It looks that I need to implement them and also to modify IdentitySessionFactory to use my implementations of this classes. That looks pretty straight forward.
I also have one more question: Do I need to implement methods in IdentitySession for creating, deleting, manging user and groups, if I don't plan to use activiti for that operation? (or I can just leave them empty)
Currently I started to do this with user/groups in database (small demo proof of concept application) letter on when I connect all to LDAP (AD) I'll send you code and LDAP structure of user and groups.
All best