The sudoers file, /etc/sudoers, controls which commands can be executed by which users. It provides a flexible way of managing the command aspect of security.
Passwordless sudo for all in the sudo group
This is really not secure. Use at your own risk
There should be a line that starts with %sudo somewhere in the file. Modify it to match the line below to allow anybody with sudo powers to use sudo without a password.
%sudo ALL=NOPASSWD: ALL