Securing your content from unrestricted access from the internet and giving multiple users access to the same content is usually done with .htaccess. Just make jour password file only accessible to the Synology users with administrative privileges.
For example just user root .
Code:
chown root:root password
chmod 600 password
The values of the options setting (wrench icon) are saved on a per browser basis.
So use different browsers or PC's to test.