code: func CertFingerprint(certPEM []byte) (string, error) {
  	p, _ := pem.Decode(certPEM)
  	if p == nil {
  		return "", errors.New("no valid PEM data found")
  	}
  	cert, err := x509.ParseCertificate(p.Bytes)
  	if err != nil {
  		return "", fmt.Errorf("failed to parse certificate: %v", err)
  	}
  	return hashutil.SHA256Prefix(cert.Raw), nil
  }
docs: // CertFingerprint returns the SHA-256 prefix of the x509 certificate encoded in certPEM.