code: def request_issuance(self, csr):
          
          action = LOG_ACME_REQUEST_CERTIFICATE()
          with action.context():
              return (
                  DeferredContext(
                      self._client.post(
                          self.directory[csr], csr,
                          content_type=DER_CONTENT_TYPE,
                          headers=Headers({b'Accept': [DER_CONTENT_TYPE]})))
                  .addCallback(self._expect_response, http.CREATED)
                  .addCallback(self._parse_certificate)
                  .addActionFinish())
docs: Request a certificate.
  
          Authorizations should have already been completed for all of the names
          requested in the CSR.
  
          Note that unlike `acme.client.Client.request_issuance`, the certificate
          resource will have the body data as raw bytes.
  
          ..  seealso:: `txacme.util.csr_for_names`
  
          ..  todo:: Delayed issuance is not currently supported, the server must
                     issue the requested certificate immediately.
  
          :param csr: A certificate request message: normally
              `txacme.messages.CertificateRequest` or
              `acme.messages.CertificateRequest`.
  
          :rtype: Deferred[`acme.messages.CertificateResource`]
          :return: The issued certificate.