[SOLVED] Unable to authenticate with pam on 16.04

I upgraded to 16.04 from 2.x, and now I can't authenticate using pam.

I switched to internal authentication as a test, and it all works fine.

I think I traced the problem to the epam helper program.

Here is my xmpp pam service file: (I added pam_warn.so to get log messages)

# File autogenerated by pamd_mimic in pam eclass

auth    required        pam_warn.so
auth    include         system-auth
account include         system-auth 

I used the pamtester program (from here: http://pamtester.sourceforge.net/) to test that, and it works fine.

pamtester -I ruser=me xmpp me authenticate
Password:
pamtester: successfully authenticated 

When I do that, this shows up in syslog:

Aug 26 10:36:29 hostname pamtester: pam_warn(xmpp:auth): function=[pam_sm_authenticate] flags=0 service=[xmpp] terminal=[] user=[me] ruser=[me] rhost=[]

But when I try to log in using Pidgin, this is what shows up in syslog:

Aug 26 10:39:20 hostname epam: pam_warn(xmpp:auth): function=[pam_sm_authenticate] flags=0 service=[xmpp] terminal=[] user=[me] ruser=[me] rhost=[]
Aug 26 10:39:20 hostname unix_chkpwd[11274]: check pass; user unknown
Aug 26 10:39:20 hostname unix_chkpwd[11275]: check pass; user unknown
Aug 26 10:39:20 hostname unix_chkpwd[11275]: password check failed for user (me)
Aug 26 10:39:20 hostname epam: pam_unix(xmpp:auth): authentication failure; logname= uid=103 euid=103 tty= ruser=me rhost=  user=me 

Notice that the first line contains the same information as the entry from pamtester, in particular the same user name.

It looks like epam isn't passing the user name correctly.

Is there any way I can see what it's doing? Or does anyone have any ideas?