Elementary OS - User permissions for internet (beginner)

[Xoxy]

How can I edit user permissions so that the user needs to type in his password to connect to the internet (Elementary Luna/Ubuntu 12.04)?
The PC is set up using LAN + a VPN server.
I'm using the "Gnome System Tools" (no command line). Although I unchecked the boxes for "Internet connection via modem" and "connect to wireless & ethernet networks" I have access to the internet and I can use the VPN without "admin" password (still need to type in keychainring).
Thank you!

EDIT: Gnome System Tools http://askubuntu.com/questions/66718/how-to-manage-users-and-groups

[coffeecat]

Elementary uses its own desktop and many different GUI apps.

Thread moved to Other OS/Distro Support.

[Xoxy]

AFAIK the applet is the same as in Ubuntu. It's the Gnome System Tools from this page: http://askubuntu.com/questions/66718/how-to-manage-users-and-groups