When I logon to my company's computer with the AD username/password, I find that my Outlook will launch successfully. That means the AD authentication has passed.
In my opinion, outlook retrieves the AD user information, then sends it to an LDAP server to verify.
But I don't know how it retrieves the information, or by some other methods?
You are right, there is an ongoing communication between your workstation and the Active Directory server, which can use LDAP protocol.
Since I don't know what you tried so far, I suggest that you look into the python module python-ldap. I have used it in the past to connect, query and modify information on Active-Directory servers.
How does auto-login Outlook successfully when in AD environment?