your post helped me to arrive at the solution with just .htaccess and .htpasswd files without editing Apache.

In the root PrivateBin folder I have the following .htaccess code added by me:

Require method GET OPTIONS
Require valid-user

AuthUserFile    /home/panelusername/public_html/domain.ext/.htpasswords/   PrivateBin/.htpasswd
AuthName "POST PASS"
AuthType Basic

Then outside of the PrivateBin folder I created an .htpassword file located at /home/panelusername/public_html/domain.ext/.htpasswords/PrivateBin/.htpasswd with the encrypted username and password.

This worked so now when user press "send" need to know credentials to see data successfully saved. ///

pastebin stikked