SLO redirect to site

[Cantor, Scott]

With or without proxying, the IdP has never and will never support any return parameters. That would turn it into an open redirector, with no obvious/prcatical means of limiting it.

Logout and proxying do not work together at present either. If we fix that, it will likely involve just blocking logout propagation and the browser would be expected to land on the real IdP in the end.

-- Scott