Run Contao CMS behind a NGINX proxy with SSL enabled

// Add this code snippet into your /web/app.php 
// respectively the index.php
// x.x.x.x being the IP of your proxy.
// You can also check this issue here for some more directions
// https://github.com/contao/core/issues/8826
Request::setTrustedProxies(['x.x.x.x'], -1);