Question about best practice regarding release of deprecated encodings

[Cantor, Scott]

Also, no, using the attribute filter in the SP doesn't really work to eliminate duplicates because you'd have to map them into separate headers (which means the duplicates aren't really duplicates anymore). Filter rules are based on the name you map the attribute into, not the name on the wire.

There is no way, full stop, to control the encodings you support by IdP without misusing a bunch of complex features in a way that would be ludicrous to consider. It's just not how the SP was designed because I did not anticipate anybody would choose to name attributes subjectively, and the cost of doing so wasn't really significant (duplicates or separate mappings).

-- Scott