Deliver a signature for a pending sign-in

Public. Accepts the EIP-4361 signature for one pending authorization request, so a wallet that is not in the browser can finish a sign-in without a human carrying the signature back by hand.

Authorised by the delivery token the consent screen puts inside the block it asks you to paste into your agent's chat. That token is a MAC over the wallet, the scopes and the approval caps, so those cannot be chosen here — the message is rebuilt from the server's own record and the token's authenticated fields, and the signature is verified against that.

One delivery per sign-in. A signature that does not verify is refused and leaves the request open, so signing again is safe; a second accepted delivery is impossible. GET is accepted on the same path for agents that cannot make a POST — same checks, same limit.