Support SAML subject-id and pairwise-id natively
subject-id and pairwise-id are replacement for SAML NameIDs in use in Renater/Edugain federations : https://docs.oasis-open.org/security/saml-subject-id-attr/v1.0/cs01/saml-subject-id-attr-v1.0-cs01.html
Currently, subject-id and pairwise-id can be enabled via a macro, but this is complex to configure. Especially pairwise-id which must be configured as a per-SP macro for all SPs
Maybe we should natively implement subject-id and pairwise-id through simple options in SAML SP configs