session_test.module

<?php


/**
 * @file
 * Test module.
 */
use Drupal\user\UserInterface;

/**
 * Implements hook_user_login().
 */
function session_test_user_login(UserInterface $account) {
    if ($account->getAccountName() == 'session_test_user') {
        // Exit so we can verify that the session was regenerated
        // before hook_user_login() was called.
        exit;
    }
    // Add some data in the session for retrieval testing purpose.
    \Drupal::request()->getSession()
        ->set("session_test_key", "foobar");
}