I have played around with nsec.app now and have looked at the nip46 code by nostr:npub107jk7htfv243u0x5ynn43scq9wrxtaasmrwwa8lfu2ydwag6cx2quqncxg in ngine: https://github.com/verbiricha/ngine/blob/main/packages/core/src/context.tsx#L222

Will use that as a starting point, when I find some time.