I'm one of the noob too when I encountered something like this. So... I set the passwords using the command security page gave me: /opt/lampp/lampp security Then I used password xyz for all the passwords... Then when I go to site/, it ask for a basic authentication. But when I tried root//xyz, it does not allow me login. So, after some digging, it turns out the xyz password was set for a default user named 'lampp'. When I tried to login using lampp//xyz, it worked like a charm.
The issue is that they made an assumption that everyone knows to use lampp//rootpw as their login o.O And... that is a basic auth for the directory! not pw for phpmyadmin or pw for mysql...