[CentOS] Setting up Samba as fileserver for existing Windows domain

This is probably covered in many places, but my Google-fu is failing.

I have an existing office of Windows computers, in a domain, with a
couple of Windows Server 2012 AD servers.  I need to add a file server,
so I'd prefer to use CentOS 7 and Samba to do it (because I know very
little about Windows).  However, I'm not finding a good how-to on that.
When I search for "samba active directory" or "samba domain", the
results are mostly about setting up Samba to be the domain controller,
or join an AD domain as a controller, which I don't really want to do if
I don't have to.

Anybody have any tips, pointers, etc.?
-- 
Chris Adams <linux at cmadams.net>