code: func (d *Data) SetIssuer(der []byte) error {
  	var err error
  	d.Issuer, err = x509.ParseCertificate(der)
  	if err != nil {
  		return err
  	}
  	return nil
  }
docs: // SetIssuer sets the issuer of a certificate
  // TODO: Validate if the correct issuer is given