brew install pam-u2f
mkdir -p ~/.config/Yubico/
pamu2fcfg > ~/.config/Yubico/u2f_keys
<Press the U2f device>
cat ~/.config/Yubico/u2f_keys # should output <your username>:<really long hash>
In /etc/pam.d/screensaver
Add to the top:
auth sufficient pam_u2f.so
In /etc/pam.d/authorization
Add to the top:
auth sufficient pam_u2f.so