Who has State Authority in Client/Host mode?

I'm very confused by state authority. I'm using Client/Host mode (AutoHostOrClient). StateAuthority on NetworkObjects always returns a PlayerRef with ID=-1, which I take to mean "no one". Doesn't matter whether I request authority or not.

Is it possible to grant exclusive authority to modify Networked properties to a particular client in this game mode? Or is that only possible in Shared mode?