I seem to recall authorized_keys works as expected; it goes into %HOME%\.ssh\authorized_keys (I'm not sure/can't recall if there are some similar permission requirements). Anyway, that's eg: c:\users\mcgyver\.ssh\authorized_keys

And ssh needs a restart.

That said, windows remote management is traditionally via WMI, not powershell. But PS has come a long way, and ssh is a sane transport. And it can function as a tunnel for WMI, RDP and PS (ssh is easier to use for key based auth, disabling password auth).