IdP entityID on IIS

[Kristof Bajnok]

Hi,

what's the canonical (default) server variable for fetching the IdP
entityId on an SP running on IIS?

One has complained that the session check in the Drupal shib_auth module
for (Shib-Identity-Provider || Shib_Identity_Provider ||
HTTP_SHIB_IDENTITY_PROVIDER) failed, he needed
'HTTP_SHIBIDENTITYPROVIDER' for this purpose.

I still need some information from him (I also don't know the IIS
version, as an example). However, could you please post a conditional
expression on server variables, from which I can determine if there's an
active SP session, and which works reliably on all supported platforms?
Actually I'm deep in dark when it's getting to Windows and IIS, so I'm
not even sure whether the $_SERVER array elements in his PHP are request
headers or environment variables (in Apache, they're both).

Thanks in advance,
Kristof