Trouble Setting Up Non-Admin Remote Access on ReadyNAS

johnackerman wrote:

I’m asking because I manage a small site and want each collaborator to securely access only their own files without using the admin account.

There are two parts to this - one is access to the network the NAS is running on, the other is authentication.

Here are the general approaches: 

1. Use port forwarding to allow anyone to reach the NAS over the internet, and rely on strong passwords for authentication and security.  If you use this approach, I'd suggest FTPS as the sharing protocol.  The disadvantage of this technique is that the NAS is EoL and uses a deprecated version of Linux.  So there is a security risk.
2. Use a VPN to access the network, and use NAS user accounts for authentication.  One risk here is that the VPN allows full access to the network.  Another is that you cannot easily remove VPN access for a collaborator when the relationship ends.  One advantage of Zerotier is that since it creates a virtual network, you can easily exclude devices on your physical network from the VPN. But it would be a bit more work for your collaborators to set up.
3. Deploy your own VPN server, and use Radius or Active Directory to authenticate users when they connect using the VPN.
4. Deploy an OwnCloud or NextCloud server for collaboration, and mount the NAS shares on that server.  (While you might be able to install OwnCloud and NextCloud on the NAS itself, given the EoL status it would be safer to use a different server platform that gets security updates).
5. If your site is already cloud-hosted, create a secured area on the web server for the collaborators to use.  Then use rsync or something similar to back up their files on the NAS.  This is the easiest method (and if your site is hosted on the NAS itself, it would be best to change that to a cloud-hosted service).