Finns en bra förklaring här:
http://blog.avisi.nl/2014/05/06/two-factor-authentication-on-osx-a-yubikey-example/
Citat:
CHANGE THE AUTHENTICATION PROCESS FOR SUDO AND USER-LOGIN
Again from the root terminal, add the line auth required pam_yubico.so mode=challenge-response to the following files:
/etc/pam.d/authorization
/etc/pam.d/sudo
For example
Edit the file:
terminal (root)
vi /etc/pam.d/authorization
Add the line:
auth required pam_yubico.so mode=challenge-response
DONE