GET /acme/cert/g7m3ZQeTEqa HTTP/1.1
  Host: example.com
  Accept: application/pem-certificate-chain

  HTTP/1.1 200 OK
  Content-Type: application/pem-certificate-chain
  Link: <https://example.com/acme/some-directory>;rel="index"
  Cert-Not-Before: Thu, 3 Oct 2019 00:00:00 GMT
  Cert-Not-After: Thu, 10 Oct 2019 00:00:00 GMT

  -----BEGIN CERTIFICATE-----
  [End-entity certificate contents]
  -----END CERTIFICATE-----
  -----BEGIN CERTIFICATE-----
  [Issuer certificate contents]
  -----END CERTIFICATE-----
  -----BEGIN CERTIFICATE-----
  [Other certificate contents]
  -----END CERTIFICATE-----