which process display a given window?

[Frantisek Hanzlik]

A few moments ago on my F15 desktop appeared window with title
"Authentication" and two user-fillable fields within, "Name" and
"Password". Nothing else.
At this moment I not expect from none of cca 15-20 running apps this
question window, nor from several running applets (thus, probably
some crackers want access to my credit cards ;)

How generally I can state which process display it?
I would expect, when right-clicking on window top title bar, some
item as e.g. "window properties" - where would be possible find info
about process displaying this window. But there isn't nothing of the
kind. Thus, is there other way discovering this?

I forgot mention, I'm now in F15 using XFCE (but IMO in Gnome window
manager has not capability too).

Thanks, Franta Hanzlik