function custom_random_pages() {
$length = 999;
$num_pages = 1000000;
for ($i = 1; $i <= $num_pages; $i++) {
$random_string = generate_random_string($length);
add_rewrite_rule(
'^' . $random_string . '/?$',
'index.php?page_id=YOUR_PAGE_ID',
'top'
);
}
}
add_action('init', 'custom_random_pages');