Openldap and memberof attribute

Hello,
I installed openldap on windows platform. I created users and one gorup.
In group attributes I can add attribute memeber and write dn of my user.
But for example when I would like to integrate it with other system and
use ldap as authentication I would like to use attribute of group. How to
add this attribute to the user. For example in AD I have attribute
memberOF. How to do it , create other attribute for my user and use it in
authentication?

BR,
Sebik