[sudo-users] sudo never prompts for password

[Todd C. Miller]

Some vendors build sudo with the exempt_group feature enabled by
default.  Try running the this on one of the affected servers:

$ sudo sudo -V | grep exempt

If you see something like:

Users in this group are exempt from password and PATH requirements: sudo

then that sudo binary has been compiled such that users in the
"sudo" group need not enter a password.

You can disable that by adding the following line to sudoers file.

    Defaults !exempt_group

 - todd