To enable LDAP authentication you need to make sure that the file /db/system/security/config.xml content something similar to that below
<security-manager xmlns="http://exist-db.org/Configuration" ...
...
ldap://directory.mydomain.com:389
...
...
ou=department,dc=directory,dc=mydomain,dc=com
some-ldap-user
some-ldap-password
(&(objectClass=user)(sAMAccountName=${account-name}))
...
..
....
....
</account
(&(objectClass=group)(sAMAccountName=${group-name}))
...
..
....
....
...
...
url - the URL to your LDAP directory server. base - the LDAP base to use when resolving users and groups