Question: would it be possible to do time based delegation? To be more clear, I mean say you have a nostr webapp that you'd like to use, so you create some delegated keys, those keys are stored in the browser (think JWT tokens) and eventually expire. And a new fresh pair can be renegotiated later. This would allow users to sign/send events using the app but without needing constant approval from the remote signer (I'm think a chat app that uses your nostr keys, it would be a pain to have to constantly use my remote signer as opposed to just using it once for a session). Is this kind of scheme possible or even advisable?