Yii2 PHP Perform checking user with beforeAction in Controller

I'm aware there's a similar post to this but just to confirm my understanding.

I just start using Yii2 PHP. I've used dektrium/yii2-user that can login and register. I want to do a beforeAction() to check logged user auth.key if exist in database (XAMPP MYSQL). Below is the code I want to performed on.

//Action direct to json.php.
    public function actionJson()
    {
        return $this->render('json');
    }

If the statement true will direct to the page, else shows a alert error.

I know the exact code is

public function beforeAction($action){}

What I'm confused on is where do I actually put beforeAction() at.

BeforeAction()

This method is invoked right before an action is executed.

https://www.yiiframework.com/doc/api/2.0/yii-base-controller#beforeAction()-detail

Where to place it?

You must place it inside your login controller (LoginController.php) class. Remember to call the parent inside the function as :

public function beforeAction($action)
{
    if (!parent::beforeAction($action)) {
        return false;
    }

    return true; // or false to not run the action
}

Then all the actions from that controller will use your custom beforeAction function.