Some of those could be handled by the device password (although apple might have dug themselves a hole with touch I'd there) - the other with an one time password generator whose secret was available to trusted ios devices? For Apple services, that might even be simplified to a callback system; mail app on desktop shows a token "bushy eyebrows", ios auth app display the token "busy eyebrows" and a login/cancel prompt. The actual auth can be done in a challenge - response fashion between the service and the ios device. Another use for the Apple watch...