separate collection for R&S IdPs

[iay]

We should build a separate identifiable collection of IdPs labelled with the R&S category support entity attribute. This will require support from MDA to allow conditionally adding net.shibboleth.metadata.ItemTag objects to items based on an XPath expression, and from mdq-server to turn all such ItemTag values into identifiable collections.

Question: Should this be based on the REFEDS R&S entity category support, or the (currently far more numerous) InCommon R&S? One possibility would be to do both.

[iay]

Initial implementation adds the following identifiers:

• collection:idps
• collection:inc-r-and-s-idps
• collection:refeds-r-and-s-idps (currently none of these exist)

The identifiers are arbitrary and this is essentially a demonstration of a more general capability.