Check for Flarum authentication before the main site even loads

index.php

<?php

if (isset($_COOKIE['flarum_remember']))
{
    $mysql = new mysqli("localhost", "flarum_sql_user", "flarum_sql_pass", "flarum_database");
    $result = $mysql->query("SELECT * FROM access_tokens WHERE id = '". $mysql->real_escape_string($_COOKIE['flarum_remember']) ."'");
    if ($result->num_rows == 0)
    {
        // Invalid cookie
        header('Location:https://my.laravel.site/login');
        exit;
    }
}
else
{
    // No cookie
    header('Location:https://my.laravel.site/login');
    exit;
}

// Rest of normal index.php here