docs: def acme_sign_certificate(common_name, size=DEFAULT_KEY_SIZE):
      '''
          Sign certificate with acme_tiny for let's encrypt
      '''
      private_key_path = '{}/{}.key'.format(CERTIFICATES_PATH, common_name)
      certificate_path = '{}/{}.crt'.format(CERTIFICATES_PATH, common_name)
      certificate_request_path = '{}/{}.csr'.format(CERTIFICATES_PATH,
                                                    common_name)
      signed_cert = '{certificates_path}/{common_name}-signed.crt'.format(
          certificates_path=CERTIFICATES_PATH,
          common_name=common_name)
  
      generate_certificate(common_name, size)
  
      cmd = 'openssl req -new -sha256 -key {private_key_path}'
      cmd += ' -subj "/CN={common_name}" -out {certificate_request_path}'
      cmd = cmd.format(
          private_key_path=private_key_path,
          common_name=common_name,
          certificate_request_path=certificate_request_path
      )
      p = subprocess.Popen(cmd,
                           shell=True,
                           stdout=subprocess.PIPE,
                           close_fds=True)
      p.communicate()
  
      _internal_sign_certificate(certificate_path, certificate_request_path,
                                signed_cert)
  
      cron = "/etc/cron.monthly/acme-renew"
      if not os.path.exists(cron):
          with open(cron, "w") as file:
              file.write("#!/bin/bash\ncozy_management renew_certificates\n")
          st = os.stat(cron)
          os.chmod(cron, st.st_mode | S_IXUSR)