I've installed my computer (Ubuntu 18.04) with an user called 'localadmin'.
Then I've created another user "thomas", which is in group sudo.
If I'am logged in as 'thomas' and a graphical program ask for sudo authentication (e.g. gedit admin:///etc/fstab),I have to enter the password for the user 'localadmin'.
In the terminal, e.g.
sudo vi /etc/fstab, the user 'thomas' will be elevated, as expected.
How can I change the graphical ui to ask for the right user for elevating?