[Samba] multiuser with simple user mapping

[Eric Levy]

I have a Linux server, and a NAS device from Synology. Both systems
have matching sets of user names. 

>From the server, I create a mount through the following command:

$ sudo mount.cifs //diskstation/usr /mnt -ouser=master,multiuser,setuids,idsfromsid

The expectation is that the particular combination of mount options
makes the ownership and permissions of files on the mount match those
on the server, with users mapped according to identity on symbolic
names.

In contrast, I observe that all the files are owned by root, and not
accessible to regular users.

How may I achieve the desired mapping of ownership and permissions,
based on user name?

Note that it is not necessary that permissions on the mount are
reported as on the NAS, which uses a non-POSIX ACL system, only that
the NAS enforces the permissions of files in the mount according to its
rules.

The NAS runs Samba 4.10.18 and the server runs version 4.11.6.

Note that as Synology tries to limit the configurability of server
shares, it is preferred to achieve the desired effect with minimal
alteration of the NAS configuration.