The simplest way is to gather the username and password, connect to your AD with Net::LDAP, and bind using the username and password. Check the result of the bind, if it was successful (!$result->code) the username and password are correct. Identifying whether that user is someone who should have permission to unlock someones account is another matter - you may want to create a group, and do a search for membership.

For encrypted authentication, you need to connect to the AD with Net::LDAPS.

The perl-ldap mailing list would be a good place to get help if you get stuck - in fact reading back through the list archives will get you a long way towards your objective.