code: def _ensure_authed(self, ptype, message):
          
          if (
              not self.server_mode
              or ptype <= HIGHEST_USERAUTH_MESSAGE_ID
              or self.is_authenticated()
          ):
              return None
          # WELP. We must be dealing with someone trying to do non-auth things
          # without being authed. Tell them off, based on message class.
          reply = Message()
          # Global requests have no details, just failure.
          if ptype == MSG_GLOBAL_REQUEST:
              reply.add_byte(cMSG_REQUEST_FAILURE)
          # Channel opens let us reject w/ a specific type + message.
          elif ptype == MSG_CHANNEL_OPEN:
              kind = message.get_text()  # noqa
              chanid = message.get_int()
              reply.add_byte(cMSG_CHANNEL_OPEN_FAILURE)
              reply.add_int(chanid)
              reply.add_int(OPEN_FAILED_ADMINISTRATIVELY_PROHIBITED)
              reply.add_string("")
              reply.add_string("en")
          # NOTE: Post-open channel messages do not need checking; the above will
          # reject attemps to open channels, meaning that even if a malicious
          # user tries to send a MSG_CHANNEL_REQUEST, it will simply fall under
          # the logic that handles unknown channel IDs (as the channel list will
          # be empty.)
          return reply
docs: Checks message type against current auth state.
  
          If server mode, and auth has not succeeded, and the message is of a
          post-auth type (channel open or global request) an appropriate error
          response Message is crafted and returned to caller for sending.
  
          Otherwise (client mode, authed, or pre-auth message) returns None.