List Active Directory Users
Why is SQL Server required to do this task?  This isn't the objective of an RDBMS.  You would have to go through hoops to get SQL Server to find this data.

The quickest/easiest/most natural way to do this?  The Active Directory PowerShell module.  It's a one-liner:

Get-ADGroupMember "administrators" | Select-Object Name, DistinguishedName, ObjectClass


In short, keep logic like this away from SQL Server and put it in the OS where it belongs.