Derive Macro signature::Verifier

#[derive(Verifier)]

This is supported on feature="derive-preview" only.

Derive the Verifier trait for a type which impls DigestVerifier.

When implementing the DigestVerifier trait for a signature type which itself impl's the DigestSignature trait (which marks signature algorithms which are computed using a Digest), signature providers can automatically derive the Verifier trait when the digest algorithm is DigestSignature::Digest (i.e. the "standard" digest algorithm for a given signature type)

This automates all of the digest computation otherwise needed for a complete signature algorithm implementation.