code: public function handle(Request $request, Closure $next) {
          /** @var Route $route */
          $route = $request->route();
          $actionInfo = $route->getAction();
          if (!empty($actionInfo['validate'])) {
              $messages = [];
              if (!empty($actionInfo['validation_messages'])) {
                  $messages = trans($actionInfo['validation_messages']);
                  if (!is_array($messages)) {
                      $messages = [];
                  }
              }
              $errors = $this->validateAndReturnErrors($request, $actionInfo['validate'], $messages);
              if (!empty($errors)) {
                  return $this->makeValidationErrorsJsonResponse($errors);
              }
          }
          return $next($request);
      }
docs: Handle an incoming request.
  
  @param  Request $request
  @param  \Closure $next
  @return mixed