Bit of a SameSite update

[Cantor, Scott]

I've been adjusting the page intro [1] a bit to reflect the fact that Chrome's breaking change has been rolling out for the last month, and will also be breaking Edge shortly.

I also finally hit an SP behaving so pathologically broken with frames and POST such that third-party cookies alone weren't enough and the SameSite change broke the IdP.

So it's starting to get real, just thought I'd note it.

-- Scott

[1] https://wiki.shibboleth.net/confluence/display/IDP4/SameSite