What's the difference between NIP-46 Nostr Signer and NIP-26 Delegation, and how can they be combined?

Both solutions deal with the scenario when you want to use a Nostr app without entering your secret key, and a 'keystore' app which only deals with your keys.

In the Signer solution, every single time the app needs a signature (posting a note, a like, a follow, etc.), it reaches out to the Signer for a signature. Communication happens over Nostr events.

In the Delegation solution, on the other hand, you first create a delegation, which allows the app to post on the behalf of the user without the secret key. Typically a delegation is restricted for some period (e.g. one month). Signing the delegation requires the key, and the delegation has to get to the app.

The two approaches can be combined: the app can request the Signer to sign a delegation, and it can use the delegation right away to post on behalf of the user, without needing to further contact the Signer.

I hope to see more apps supporting both NIP-46 and NIP-26 in the future.