You're asking for your users to be able to login in using DOMAIN\user which tells me that you are running a domain on your network. Why not join the NAS to AD? The NAS will automatically migrate your users.
Also, the permissions you seek can be found in the App Center. Choose the app you want to set permissions for by clicking the drop down arrow >> Display On menu item.
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The problem is that some of these apps are not compatible with AD permissions. There are some Q mobile apps that do not allow you to log on using domain credentials (although there are some that do), for instance.
The NAS can indeed be set as domain controller/DNS Server. I haven't tried successfully as I'm probably seeing the same thing as you are. I'm going to say that I just don't know how to do it on QTS.
I usually have my NAS joined to domain as client, but haven't done so after beta. Haven't found the time.
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