/etc/pam.d/sshd
#@include common-auth
...
auth required pam_google_authenticator.so nullok


/etc/ssh/sshd_config
...
ChallengeResponseAuthentication yes
...
AuthenticationMethods publickey,keyboard-interactive

$ ssh ubuntu@server
ubuntu@server: Permission denied (keyboard-interactive).

Aug 17 11:40:31 ip-10-0-0-182 sshd(pam_google_authenticator)[6834]: debug: start of google_authenticator for "ubuntu"
Aug 17 11:40:31 ip-10-0-0-182 sshd[6832]: error: PAM: Permission denied for ubuntu from X.X.X.X
Aug 17 11:40:32 ip-10-0-0-182 sshd[6832]: Connection closed by authenticating user ubuntu X.X.X.X port 61076 [preauth]