class AccessDeniedSubscriber

class AccessDeniedSubscriber extends HttpExceptionSubscriberBase {
    
    /**
     * The current user.
     *
     * @var \Drupal\Core\Session\AccountInterface
     */
    protected $account;
    
    /**
     * Constructs a new redirect subscriber.
     *
     * @param \Drupal\Core\Session\AccountInterface $account
     *   The current user.
     */
    public function __construct(AccountInterface $account) {
        $this->account = $account;
    }
    
    /**
     * {@inheritdoc}
     */
    protected function getHandledFormats() : array {
        return [
            'html',
        ];
    }
    
    /**
     * {@inheritdoc}
     */
    protected static function getPriority() : int {
        // Use a higher priority than ExceptionLoggingSubscriber, because there's
        // no need to log the exception if we can redirect.
        // @see Drupal\Core\EventSubscriber\ExceptionLoggingSubscriber
        return 75;
    }
    
    /**
     * Redirects users when access is denied.
     *
     * @param \Symfony\Component\HttpKernel\Event\ExceptionEvent $event
     *   The event to process.
     */
    public function on403(ExceptionEvent $event) : void {
        $route_name = RouteMatch::createFromRequest($event->getRequest())
            ->getRouteName();
        $redirect_url = NULL;
        if ($this->account
            ->isAuthenticated()) {
            switch ($route_name) {
                case 'user.login':
                    // Redirect an authenticated user to the profile page.
                    $redirect_url = Url::fromRoute('entity.user.canonical', [
                        'user' => $this->account
                            ->id(),
                    ], [
                        'absolute' => TRUE,
                    ]);
                    break;
                case 'user.register':
                    // Redirect an authenticated user to the profile form.
                    $redirect_url = Url::fromRoute('entity.user.edit_form', [
                        'user' => $this->account
                            ->id(),
                    ], [
                        'absolute' => TRUE,
                    ]);
                    break;
            }
        }
        elseif ($route_name === 'user.page') {
            $redirect_url = Url::fromRoute('user.login', [], [
                'absolute' => TRUE,
            ]);
        }
        elseif (in_array($route_name, [
            'user.logout',
            'user.logout.confirm',
        ], TRUE)) {
            $redirect_url = Url::fromRoute('<front>', [], [
                'absolute' => TRUE,
            ]);
        }
        if ($redirect_url) {
            $event->setResponse(new RedirectResponse($redirect_url->toString()));
        }
    }

}