mage2login.php

<?php
namespace mage2login;
 
use Magento\Customer\Model\ResourceModel\CustomerRepository;
use Magento\Customer\Model\Session;
use Magento\Framework\App\ObjectManager;
use Magento\Framework\App\State;
 
if (!isset($_REQUEST['id']) || !is_numeric($_REQUEST['id'])) {
    echo "Usage: {$_SERVER['REQUEST_URI']}?id=%CUSTOMER_ID%";
    die();
}
 
if (is_file(__DIR__ . '/app/bootstrap.php')) {
    require __DIR__ . '/app/bootstrap.php';
} elseif (is_file(__DIR__ . '/../app/bootstrap.php')) {
    require __DIR__ . '/../app/bootstrap.php';
} else {
    die('Can't find bootstrap.php');
}
\Magento\Framework\App\Bootstrap::create(BP, $_SERVER);
$om = ObjectManager::getInstance();
 
$om->get(State::class)->setAreaCode('frontend');
$session = $om->get(Session::class);
 
$customer = $om->get(CustomerRepository::class)->getById($_REQUEST['id']);
 
if ($session->loginById($customer->getId())) {
    echo "You was logged in";
} else {
    echo "You wasn't logged in";
}