injecting a custom bean into a metadata filter

[Rod Widdowson]

TL;DR - bung it in a separate file and point services.xml at it, just as you would any other native syntax.

> Hmm, I'm still missing something I'm afraid.

We do not allow custom syntax to be mixed with native syntax in V3.   There are several places where both native and custom syntax
have to be intermixed (eg[1]) and in support of that you can put the native syntax beans in several places[1].  Global.xml is an
obvious one but that suffers from lack of reloadability, so it would be more usual to bung it into a separate file [2] and point at
it from services.xml[3],[4].

You might want to skim over [5] again

[1] https://wiki.shibboleth.net/confluence/display/IDP30/PredicateConfiguration
[2] https://wiki.shibboleth.net/confluence/display/IDP30/SpringConfiguration
[3] https://wiki.shibboleth.net/confluence/display/IDP30/ReloadableServices
[4]
http://git.shibboleth.net/view/?p=java-identity-provider.git;a=blob;f=idp-conf/src/main/resources/conf/services.xml;h=e04ac8f0afceb2
d3afec9f0acbf2ed6c02a81a2c;hb=HEAD
[5] https://wiki.shibboleth.net/confluence/display/IDP30/Configuration#Configuration-ConfigurationOverviewsandReferences