front-channel SLO iframe cross-origin problem

[Cantor, Scott]

> Using Google Chrome (Version 47.0.2526.111), everything works fine until
> the point where the JS script tries to read the content of the iframe
> (system\views\logout\propagate.vm).
> At that point I get: Failed to read the 'contentDocument' property from
> 'HTMLIFrameElement': Blocked a frame with origin "http://idp.example.com
> <http://idp.example.com/> " from accessing a cross-origin frame
> "http://sp1.example.com <http://idp.example.com/> ".

I've tested with Chrome before. The final result in the frame is either going to be back at the IdP, preventing the need for cross-origin access, or the JS should be treating it as a failed result for that SP. If it throws a fatal error while it polls for the final result to come back and pops up some box, that's never going to work, but it didn't do that when I tested it.

-- Scott