Comment # 9 on bug 1081947 from Franck Bui

(In reply to Josef M�llers from comment #8)
> (In reply to Franck Bui from comment #7)
> > (In reply to Josef M�llers from comment #6)
> > > Re comment #3:
> > > Why should it be in the stack?
> > 
> > where else would you want to it to be ?
> 
> But how should it end up there? AFAIK the only way is to explicitly call
> pam-config!
> 

Not for basic/core modules.

AFAICS by default /etc/pam.d/common-session contains:

> session required        pam_limits.so
> session required        pam_unix.so     try_first_pass
> session optional        pam_umask.so
> session optional        pam_env.so
> session optional        pam_systemd.so

IIUC none of these modules rely on an external package to set them up.

And I just realized that even pam_systemd is part of this "core" list... I
didn't know that and I guess the use of "pam-config" in systemd.spec becomes
useless...

Perhaps you should have a look at how other distros made it ?