When set to forward_pass entering only PIN doesn't allow next level to prompt for login

_From @ThomasHabets on October 10, 2014 8:6_

Original [issue 139](https://code.google.com/p/google-authenticator/issues/detail?id=139) created by shinji@elite-systems.org on 2012-01-24T21:33:02.000Z:

I don't have any additional modules to pass the login to so I setup pam_unix to handle the second part. However if you only enter a pin then the login fails since pam_unix doesn't bother to prompt. Is there any way to allow pam_unix to prompt for a password if only a pin was entered for pam_google_authenticator? i.e. if the forwarded password doesn't authenticate the user?

Configurations:

/etc/pam.d/common-auth
auth [success=1 default=ignore] pam_unix.so nullok_secure try_first_pass
auth requisite pam_deny.so
auth required pam_permit.so
auth optional pam_ecryptfs.so unwrap

/etc/pam.d/sshd
auth required pam_env.so # [1]
auth required pam_env.so envfile=/etc/default/locale
auth required pam_google_authenticator.so nullok forward_pass
@include common-auth
account required pam_nologin.so
@include common-account
@include common-session
session optional pam_motd.so # [1]
session optional pam_mail.so standard noenv # [1]
session required pam_limits.so
@include common-password

_Copied from original issue: google/google-authenticator#138_