Slight shift of topic as well...but:

How does lightDM even handle different authentication types? KDM has a
plugin system which handles different auth types (fingerprint,
winbindd, etc.).

However, the fundamental flaw that I can see..is that at some level or
another, the UI/Greeter *has* to know what type of authentication type
it is. That is why KDM has plugins which wrap around PAM(sort of), so
that the interface can properly accommodate for the changes in auth
type. Note these plugins apply to the screensaver unlock dialog as
well.

I've been toying with the idea in my head, of using the same Plasma
plugin (actually an applet + dataengine which wraps around a main,
more generic dataengine) in tandem with the Plasma integration with
the screensaver, that is currently present. I think it'd be quite
trivial for me to do this, too -- since I specifically tried to not
make assumptions.

The plugins exist (both in the plasma frontend and regular kfrontend)
so that when it's in fingerprint mode..it won't show a textbox or any
useless stuff like that, and may additionally show a diagram of some
bloke wiping their finger across. (that's what the kdm plugin does
actually).

Anyone familiar with the structure in lightDM care to enlighten?

-- 
Shaun Reich,
KDE Software Developer (kde.org)