LegacySessionTestController.php

<?php

declare (strict_types=1);
namespace Drupal\session_test\Controller;

use Drupal\Core\Controller\ControllerBase;

/**
 * Controller providing page callbacks for legacy session tests.
 */
class LegacySessionTestController extends ControllerBase {
    
    /**
     * Prints the stored session value to the screen.
     */
    public function get() : array {
        return empty($_SESSION['legacy_test_value']) ? [] : [
            '#markup' => $this->t('The current value of the stored session variable is: %val', [
                '%val' => $_SESSION['legacy_test_value'],
            ]),
        ];
    }
    
    /**
     * Stores a value in $_SESSION['legacy_test_value'].
     *
     * @param string $test_value
     *   A session value.
     */
    public function set(string $test_value) : array {
        $_SESSION['legacy_test_value'] = $test_value;
        return [
            '#markup' => $this->t('The current value of the stored session variable has been set to %val', [
                '%val' => $test_value,
            ]),
        ];
    }

}