I never had an issue with authentication. My issue was a typo in sudoers (I allowed a user to view syslog, iirc, and had a semicolon instead of a colon) that prevented me from using sudo, as only my primary user was allowed to log in via ssh. Fortunately cloud vps still has vnc login, and I actually had a root password. Now I use a root shell to edit sudoers, so I can test it before dropping root.

You should use "visudo", which opens the file in the default editor, then validates it before saving.

But make sure to change the default editor to something sane first. (* ducks *)

:q!dammitwtf

+1 to that!

I like nano, and I'm not ashamed to admit it.

if you edit outside of visudo, you can run visudo -cf <filename>.

example: visudo -cf /etc/sudoers visudoe -cf /etc/sudoers.d/extra

Yeah, cannot say I've never done that.

Test then Ban.