i had to this for webrtc calls before, and I ended up managing it all server side (there was a shared game state on the server, so it was fine).

Although, LocalStorage is the best way i've seen to handle the situation in a single page app, where you log out on one of the open tabs, and the other ones still think they are still logged in.

In general, there's a lot of really "fun" edge cases when it comes to modern web apps and multiple open instances ...