code: function stored(err, state) {
          if (err) { return self.error(err); }
          if (!state) { return self.error(new Error('Unable to generate required state parameter')); }
  
          params.state = state;
          var location = config.authorizationURL + '?' + querystring.stringify(params);
          self.redirect(location);
        }
docs: State Storage/Management