Simple TYPO3 Authentication service

ext_localconf.php

<?php
\TYPO3\CMS\Core\Utility\ExtensionManagementUtility::addService(
        'your_service_key',
        'auth',
        \YourName\YourExtension\Services\MagicLinkAuthenticationService::class,
        [
            'title' => 'Login via POST',
            'description' => '',
            'subtype' => 'getUserFE,authUserFE',
            'available' => true,
            'priority' => 10,
            'quality' => 50,
            'os' => '',
            'exec' => '',
            'className' => \YourName\YourExtension\Services\MagicLinkAuthenticationService::class
        ]
    );

YourName-Services-AuthenticationService.php

<?php
namespace YourName\YourExtension\Services;

use TYPO3\CMS\Core\Session\Backend\Exception\SessionNotCreatedException;
use TYPO3\CMS\Core\Database\ConnectionPool;
use TYPO3\CMS\Core\Database\Connection;
use Psr\Http\Message\RequestInterface;
use TYPO3\CMS\Core\Database\Query\QueryBuilder;
use TYPO3\CMS\Core\Http\ServerRequest;
use TYPO3\CMS\Core\Http\ServerRequestFactory;
use TYPO3\CMS\Frontend\Authentication\FrontendUserAuthentication;
use TYPO3\CMS\Core\Utility\GeneralUtility;

class StupidAuthenticationService extends FrontendUserAuthentication
{
    const SERVICE_KEY = 'YourName\YourExtension\Services\StupidAuthenticationService';
    protected $info = [];
    protected $subType = '';
    protected $loginData = '';
    protected $authInfo = [];
    protected $feUserAuth;
    protected RequestInterface $request;

    public function getServiceKey(): string
    {
        return self::SERVICE_KEY;
    }

    public function init(): bool
    {
        return true;
    }

    public function initAuth(
        string $subType,
        array $loginData,
        array $authInfo,
        FrontendUserAuthentication $feUserAuth
    ): void {
        $this->subType = $subType;
        $this->loginData = $loginData;
        $this->authInfo = $authInfo;
        $this->feUserAuth = $feUserAuth;
    }

    public function getUser()
    {
        $user = null;
      
        if (isset($_POST['mySecretParameter'])) {
            $user = $this->fetchUserBy($_POST['mySecretParameter']);
        }  

        return ($user) ? $user : false;
    }

    public function authUser(array $user): int
    {
        if (isset($_POST['mySecretParameter'])) {
            $user = $this->fetchUserBy($_POST['mySecretParameter']);
            if ($user) {
                return 200;
            }
        }  

        // Return 100. User is NOT logged in yet, but further services may still try to authenticate the user.
        return 100;
    }

    protected function fetchUserBy($uriParameter): ?array
    {
        $queryBuilder = GeneralUtility::makeInstance(ConnectionPool::class)
            ->getQueryBuilderForTable($this->user_table);
        $uriParameter = 

        $result = $queryBuilder
          ->select('*')
          ->from($this->user_table)
          ->where(
            $queryBuilder->expr()->eq('uid', $queryBuilder->createNamedParameter($uriParameter, Connection::PARAM_INT))
            )
          ->setMaxResults(1)
          ->executeQuery();

        return ($result->rowCount() > 0) ? $result->fetchAllAssociative()[0] : null;
     }

    protected function getRequest(): ServerRequest
    {
        return $GLOBALS['TYPO3_REQUEST'] ?? ServerRequestFactory::fromGlobals();
    }
}