You can use LDAP, do a search for ldap while on your moodle server.
Active Directory is a database based system that provides authentication, directory, policy, and other services in a Windows environment
LDAP (Lightweight Directory Access Protocol) is an application protocol for querying and modifying items in directory service providers like Active Directory, which supports a form of LDAP.
Short answer: AD is a directory services database, and LDAP is one of the protocols you can use to talk to it.
You should be able to find it here: http://yourmoodleserver.com/admin/auth_config.php?auth=ldap
All the best,
For more information read the forum posting: