Function request_digest 

pub fn request_digest(signed_request_body: &[u8]) -> RequestDigest

The request digest a response binding carries when the request was signed: SHA-256 over the request body exactly as it travelled, the whole COSE message (tag, headers, signature and all), marked RequestKind::Signed. The caller passes the received body, never a re-encoding of it.

For an unsigned request, use request_digest_unsigned, which also binds the client’s Cratestack-Nonce.