"Attribute Authority" configuration

[Rod Widdowson]

I wasn't aware of this, but I guess it makes sense.

In V2, the Relying Party Configuration (specifically the
ProfileConfigurations for SAML1 and SAML2) allow the specification of an
AttributeAuthority.  
This is a string which is the Id of a service (The V2 thing) which itself
carries the Id of the AttributeFilter service and the AttributeResolver
Service.  These default to the services pulled from "attribute-filter.xml"
and "attribute-resolver.xml".  Hence with no typing you get what is
expected.

Before I spend too much time bottoming this out and working out how we might
do this in V3 a few questions:

- Do we intend continuing support of this via relying-party.xml?
- If so has anyone had any thoughts on how this might be implemented?

and as a bonus question:

- Do we intend supporting multiple attribute filters or attribute resolvers
any way other than by explicit editing in
idp-conf/src/main/resources/system/*.xml

There are several ways we could achieve multiple "Attribute Authorities",
but I need to attain a zen-like trance in order to keep the two (old and
new) designs in my head and to correctly dereference services referencing
services referencing beans on the one side and beans referencing beans
referencing service on the other and I'd sooner avoid that if someone has
already done the hard work.

/Rod