code: function (req, res, next) {
              if (options.forceAuthorize) {
                  return next();
              }
              var userId = req.oauth2.user.id;
              var clientId = req.oauth2.client.id;
              var scope = req.oauth2.req.scope;
              models.Permissions.isAuthorized(clientId, userId, scope,
                  function (err, authorized) {
                      if (err) {
                          return next(err);
                      } else if (authorized) {
                          req.oauth2.res = {};
                          req.oauth2.res.allow = true;
                          server._respond(req.oauth2, res, function (err) {
                              if (err) {
                                  return next(err);
                              }
                              return next(new AuthorizationError('Unsupported response type: '
                                  + req.oauth2.req.type, 'unsupported_response_type'));
                          });
                      } else {
                          next();
                      }
                  });
          }
docs: Check if the user has granted permissions to the client app