IF condition in .htaccess or .conf files - internal or external request

Hello!

I'm going to implement interesting thing in my web server configuration.
So, the main requirement is:
1) Allow access to some directory if user clicked on a link on the same site
2) Ask about login and password if request was direct, like written directly in web browser's URL window.
Something like:

<Directory /var/www/html/restricted>
   <If "request was not direct">
       AuthType Basic
       AuthName "Restricted Content"
       AuthUserFile /etc/apache2/.htpasswd
       Require valid-user
   </If>
</Directory>

Code (ApacheConf):

Can someone help me with it?

 

This approach is not secure, the HTTP_REFERER value cannot be trusted. There is always some way to modify the value.