code: def _message_from_sr(self, token: Text, payload: Any) \
              -> Optional[BaseMessage]:
          
  
          page = self.settings()
          secret = page['app_secret']
  
          try:
              sr_data = SignedRequest.parse(token, secret)
          except (TypeError, ValueError, SignedRequestError) as e:
              return
  
          return self._make_fake_message(
              sr_data['psid'],
              page['page_id'],
              payload,
          )
docs: Tries to verify the signed request