I have user accounts for user A and user B. Both users are member of the "sudo" group which is allowed to sudo (standard setting for Kubuntu 16.04.3 LTS). Sometimes user A is already logged in and want me to do some administrative stuff.
But I only know the password for user B. I don't want to set a root password, if possible to stick to the distribution standard. Modifing /etc/sudoers would be fine.
How can I use sudo to ask for the password for user B if I'm logged in as user A?