code: func (c *Certifier) Revoke(cert []byte) error {
  	certificates, err := certcrypto.ParsePEMBundle(cert)
  	if err != nil {
  		return err
  	}
  
  	x509Cert := certificates[0]
  	if x509Cert.IsCA {
  		return fmt.Errorf("certificate bundle starts with a CA certificate")
  	}
  
  	revokeMsg := acme.RevokeCertMessage{
  		Certificate: base64.RawURLEncoding.EncodeToString(x509Cert.Raw),
  	}
  
  	return c.core.Certificates.Revoke(revokeMsg)
  }
docs: // Revoke takes a PEM encoded certificate or bundle and tries to revoke it at the CA.