[SSSD-users] uid -> sid mapping in Samba with sssd

It wasn't obvious from the documentation whether with sssd-libwbclient (only, ie
without sssd-winbind-idmap installed and configured in smb.conf, since sssd-winbind-idmap
is not available in most versions of RHEL7 as it was only recently added),

Samba's uid_to_sid(function) can always do the lookup uid_to_sid to AD if using
winbind but it wasn't clear whether this would work with sssd-libwbclient (only)
installed and what additional Samba configuration is needed for that.

Without this  the owner of a file (viewed from the WIndows client) from Explorer GUI looks
like
"Unix user\10000" rather than "user@domain" (as it would for Windows
to Windows, or if Winbind were running on the Samba server joined to AD)