Comment 5 for bug 863630

I have the same problem.

Possibly related to /etc/pam.d/lightdm-autologin being used instead of /etc/pam.d/lightdm (as in 0.9.8), since if I copy the latter to the former the error message changes from "Authentication failure" to "Conversation error":

[+3.82s] DEBUG: pam_start("lightdm-autologin", "lightdm") -> (0x66b9f0, 0)
[+3.82s] DEBUG: Starting session lightdm-gtk-greeter as user lightdm logging to /var/log/lightdm/x-0-greeter.log
[+3.84s] DEBUG: Greeter user got prompt, aborting authentication
[+3.84s] DEBUG: pam_authenticate(0x66b9f0, 0) -> 19 (Conversation error)
[+3.84s] DEBUG: Greeter user failed authentication

I had originally created /etc/pam.d/lightdm by simply copying /etc/pam.d/wdm, and never needed the lightdm-autologin file until now. It might be useful if the tarball included sample PAM files, or at least documented them.