metadata-driven attribute definition

[Peter Schober]

* Joshua Dachman <jdachman at gmail.com> [2019-07-14 23:00]:
> The idea is to be metadata-driven here. Yes, the same can currently be
> achieved through addition of tags in attribute-resolver.xml, but then every
> time an SP desires a custom mapping it must be added there rather than in
> the SP's metadata.

So far I found adding another AttributeEncoder with a relyingParties
XML attribute to be sufficient and easy to do.

-peter