code: func (s *CertificatesService) DownloadCertificate(accountID, domainIdentifier string, certificateID int64) (*certificateBundleResponse, error) {
  	path := versioned(certificatePath(accountID, domainIdentifier, certificateID) + "/download")
  	certificateBundleResponse := &certificateBundleResponse{}
  
  	resp, err := s.client.get(path, certificateBundleResponse)
  	if err != nil {
  		return nil, err
  	}
  
  	certificateBundleResponse.HttpResponse = resp
  	return certificateBundleResponse, nil
  }
docs: // DownloadCertificate gets the PEM-encoded certificate,
  // along with the root certificate and intermediate chain.
  //
  // See https://developer.dnsimple.com/v2/certificates#downloadCertificate