Have you checked what user OpenSSH usually runs as on a linux machine in order to allow key-based authentication? I'll give you a hint: it's root. That's no different than running as SYSTEM on Windows.
As a sibling comment mentioned, it makes perfect sense that the ability to create a user session requires a certain privilege. What struck me as odd, was that it only needed this on Windows when using key-based authentication - not when allowing password-based login.
AFAIK ssh needs access to /etc/shadow on Linux, if you want to use system passwords. But also, AFAIK, nothing stops you from running ssh in a chroot, without any such access (well, access to a /etc/shadow under the chroot probably).
AFAIK ssh needs access to /etc/shadow on Linux, if you want to use system passwords. But also, AFAIK, nothing stops you from running ssh in a chroot, without any such access (well, access to a /etc/shadow under the chroot probably).