code: func (s *bccspCryptoSigner) Sign(rand io.Reader, digest []byte, opts crypto.SignerOpts) ([]byte, error) {
  	return s.csp.Sign(s.key, digest, opts)
  }
docs: // Sign signs digest with the private key, possibly using entropy from
  // rand. For an RSA key, the resulting signature should be either a
  // PKCS#1 v1.5 or PSS signature (as indicated by opts). For an (EC)DSA
  // key, it should be a DER-serialised, ASN.1 signature structure.
  //
  // Hash implements the SignerOpts interface and, in most cases, one can
  // simply pass in the hash function used as opts. Sign may also attempt
  // to type assert opts to other types in order to obtain algorithm
  // specific values. See the documentation in each package for details.
  //
  // Note that when a signature of a hash of a larger message is needed,
  // the caller is responsible for hashing the larger message and passing
  // the hash (as digest) and the hash function (as opts) to Sign.