SSSD is as much (or more) about identity than access, so an ID Card type of logo can also be used.
Yeah. Good point too, thanks. The one metaphor that comes to mind is the military style id-tags or business/airline etc style name + photo tag/card hung around the neck. This however might conflict a bit with the Dogtag Certificate System logo which uses the military tag metaphor. I'll give it a few more cycles with Garrett and lets see what works.
Here's a quick sketch with simplified shape that incorporates the key as part of the letter d shape: http://www.tigert.com/designspace/key-letterd.png - I think it might work too.
Comments welcome as always :)
//Tuomas