Hi,
I doubt that SAP will provide documentation for product that is made by other company. I assume that by SAP you mean some software from SAP that is based on ABAP AS. It's also not clear which way you want to integrate. Do you want to provision users to SAP or use SAP system as source of users?
For provisioning users to SAP I quickly checked and it seems to be based around Active Directory. AD is basically LDAP so I would look into synchronizing users between LDAP and ABAP. E.g. this page could be a good start:
Synchronization of SAP User Administration with an LDAP-Compatib - Identity Management - SAP Library
But It's possible that there is a standard adapter for this from Microsoft.
For other way around this blog seems to have some info.
Cheers