Secure FTP zip file permalink

Hello,
I got the problem, that we are publishing our software on our wordpress site. The software is only visible for logged in users.
But if someone got the full permalink eg. wordpress/downloads/dl/software.zip he can download the software even if he isn’t logged in.
The next Problem is, that we have no access to the apache server, cause it is just a webspace.
I tried it with .htaccess and .htpasswd but than there is just one user but then our customers have to know this. A solution would be a .htpasswd file with a connection/anchor with the wp_users table, but i have no idea how to do this…
So in short, we want that only logged in wordpress users can download a zip from ftp.
Greetings and thanks.