docs: def _login_request(self, username=None, secret=None):
          """Send a login request with paramerters."""
          url = 'http://' + self._host + '/login_sid.lua'
          params = {}
          if username:
              params['username'] = username
          if secret:
              params['response'] = secret
  
          plain = self._request(url, params)
          dom = xml.dom.minidom.parseString(plain)
          sid = get_text(dom.getElementsByTagName('SID')[0].childNodes)
          challenge = get_text(
              dom.getElementsByTagName('Challenge')[0].childNodes)
  
          return (sid, challenge)