to make it short. you can authenticate against active directory with ldap. Active directory is an ldap server with some extensions. so MS did the same as usual. take existing ideas, add something new and start the marketing..
i wrote an ldap plugin, which is available here. if you have any questions regarding this topic, do not hesitate to contact me.
https://vborg.vbsupport.ru/showthread.php?t=148573
maybe i did not understand the question? when authenticating it doesnt matter if the password is md5, sha or any other hash.
-malc