At least until js/wasm starts using browser LocalStorage or something.
But for the foreseeable future, any login from a browser should
be considered ephemeral as the tab can close at any time and lose
the wireguard key, never to be seen again.
Updates #3157
Change-Id: I6c410d86dc7f9f233c3edd623313d9dee2085aac
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>