code: func VerifyCertificateError(cert *x509.Certificate) (revoked, ok bool, err error) {
  	if !time.Now().Before(cert.NotAfter) {
  		msg := fmt.Sprintf("Certificate expired %s\n", cert.NotAfter)
  		log.Info(msg)
  		return true, true, fmt.Errorf(msg)
  	} else if !time.Now().After(cert.NotBefore) {
  		msg := fmt.Sprintf("Certificate isn't valid until %s\n", cert.NotBefore)
  		log.Info(msg)
  		return true, true, fmt.Errorf(msg)
  	}
  	return revCheck(cert)
  }
docs: // VerifyCertificateError ensures that the certificate passed in hasn't
  // expired and checks the CRL for the server.