code: func (c *CertificateService) get(certURL string) ([]byte, string, error) {
  	if len(certURL) == 0 {
  		return nil, "", errors.New("certificate[get]: empty URL")
  	}
  
  	resp, err := c.core.postAsGet(certURL, nil)
  	if err != nil {
  		return nil, "", err
  	}
  
  	cert, err := ioutil.ReadAll(http.MaxBytesReader(nil, resp.Body, maxBodySize))
  	if err != nil {
  		return nil, "", err
  	}
  
  	// The issuer certificate link may be supplied via an "up" link
  	// in the response headers of a new certificate.
  	// See https://tools.ietf.org/html/draft-ietf-acme-acme-12#section-7.4.2
  	up := getLink(resp.Header, "up")
  
  	return cert, up, err
  }
docs: // get Returns the certificate and the "up" link.