Recently I was unable to SSH into a host where 2FA was setup via Google Authenticator.  The error message looked something like this:

```
$ ssh someuser@some.host.foo
someuser@some.host.foo's password:
Permission denied, please try again.
```

No entries were made in `auth.log`, and nothing had changed on the system aside from doing a dist-upgrade.  Thanks to [DigitalOcean](https://www.digitalocean.com/community/tutorials/how-to-set-up-multi-factor-authentication-for-ssh-on-ubuntu-16-04), I determined one update was needed in `/etc/ssh/sshd_config`.

```
## Updated to 'yes' for 2FA - int0x80
# ChallengeResponseAuthentication no
ChallengeResponseAuthentication yes
```

¯\\_(ツ)_/¯