Hello! We had to do the same thing. In our system, we didn't have the ability to query LDAP directly. It was stored in a datamart somewhere so what we did was query the datamart to get the users that were a part of the LDAP group. So however you can find to query these LDAP groups to get a list of users at your company, that is step 1. In your query, you need to be sure to bring the login back that you would normally put in your section access : 'domain\login' if necessary. Ours is just loginid, this column will be called 'NTNAME'. Make sure to also bring 'USER' or 'ADMIN' back in a column named 'ACCESS'. Once you have this detail, you just plug it into your section access:
SECTION Access;
Query here, remember that this must all be uppercase (UPPER everything data and column names, column name 'ACCESS' and 'NTNAME' at a minimum.)