Access admin only from subdomain

Hi,

I found some posts about this topic (e.g. Map wp-admin as subdomain), but they have been posted a couple of years ago and the linked resources are not available anymore (nor have I found the answers using Google).

What I am trying to do: I have a WordPress site on http://www.mysite.com and don’t want to access the backend via http://www.mysite.com/wp-admin or http://www.mysite.com/wp-login.php but rather from https://admin.mysite.com (or http://admin.mysite.com if that’s easier).

Is that something you can achieve via rewrite/proxy rules in .htaccess?

Many thanks for your support!