this is something you would need to handle manually. Hestia brings it’s own nginx (usr/local/hestia/nginx) for the panel itself, so you would need to add something to that config - however, afaik there is no general include rule for any custom file, so changes there probably get lost on the next update.
I’d suggest to proxy the panel through the regular nginx with a custom conf/template and add basic auth in there. this allows to get rid of the extra port as well (or better said to keep it internal).