// the hash (as digest) and the hash function (as opts) to Sign.
	Sign(rand io.Reader, digest []byte, opts SignerOpts) (signature []byte, err error)
}

// SignerOpts contains options for signing with a [Signer].
type SignerOpts interface {
	// HashFunc returns an identifier for the hash function used to produce
	// the message passed to Signer.Sign, or else zero to indicate that no