A couple of answers Point to sudo without a seperate user Password. You should be Aware that this will decrease your security.
For a user that already authenticated strongly with a certificate this might not be an issue because he is in posession of the certificate that theoretically could make him root.
However if you think about vulnerabilites that will provide an attacker with a limited user shell and this user has NOPASSWD set in the sudoers file the attacker is root without having any credentials to the System at all.
If sudo requires a password from the user the attacker needs time and luck to escalate his privileges to root.