I'm using this guide to install Laravel into a legacy application. I copied all legacy files into a single legacy directory, installed a new Laravel 8 project (server doesn't use PHP8 yet so can't use L9) and copied the legacy directory into the Laravel directory. I then followed the steps to make changes to the routes/web.php file, created the LegacyController and called the legacy application's index.php file.

web.php;

Route::any('{path}', LegacyController::class)->where('path', '.*');

LegacyController.php

<?php

namespace App\Http\Controllers;

use Illuminate\Http\Response;

class LegacyController extends Controller
{
    public function __invoke()
    {
        ob_start();
        require app_path('Http') . '/legacy.php';
        $output = ob_get_clean();

        return new Response($output);
    }
}

app\Http\legacy.php;

<?php

require __DIR__ . '/../../legacy/Website/index.php';

The legacy website uses a custom CMS which is loaded in its index.php file. In short, it parses the URL to get the slug, according to which it looks up if a page exists with that slug. If so it looks up the component belonging to the page (components are basic PHP files) and loads them using include_once. If a page isn't found, it redirects the user to /404.

There are some .htaccess rules to allow for "friendly" URLs etc;

# Enable the rewrite engine
RewriteEngine On
RewriteBase /website.tld

# SSL Redirect 301 transfer the current request.
RewriteCond %{HTTPS} off
RewriteRule (.*) https://%{HTTP_HOST}%{REQUEST_URI} [R=301,L]

# never rewrite for existing files, and links
RewriteCond %{REQUEST_FILENAME} -f [OR]
RewriteCond %{REQUEST_FILENAME} -l
RewriteRule ^ - [L]

# For Friendly URLs
RewriteRule ^ index.php [L]

However this .htaccess file doesn't seem to be loaded at all, as existing files (for example, PDF files but also links to CSS and JS files) are all treated as having to be routed through the CMS and thus resulting in a redirect to the 404 page.

To test whether or not the .htaccess file is loaded I added

ErrorDocument 200 "Hello. This is your .htaccess file talking."
RewriteRule ^ - [L,R=200]

to the file as described here, and as expected nothing happens. When I add the same lines to Laravel's .htaccess file in the public directory, I do get the message.

There are some other issues with other existing CMS pages not being found, but I feel like this all happens because the .htaccess file is not being used.

How can I make sure the legacy application's .htaccess file is properly used by Laravel?