Signs a single proof with the provided private key if required.
A proof to sign.
A single private key (hex string or Uint8Array).
Optional
Required for SIG_ALL proofs; not accepted for SIG_INPUTS proofs.
Signed proofs.
Will only sign if the proof requires a signature from the key.
Error if signature is not required, proof is already signed, a message is missing for a SIG_ALL proof, or given for a SIG_INPUTS proof.
Signs a single proof with the provided private key if required.