Supported credential types

[Rod Widdowson]

> DSA is extremely unusual. But you'll have to wait for Brent or Rod to
answer if
> it's not documented.

It will need to wait for Brent, I can only really speak authoritatively
about the old legacy relying-party.xml (and to answer that:  it’s the
Metadata Trust Engines which are not supported (sec:MetadataExplicitKey,
sec:MetadataExplicitKeySignature, sec:MetadataPKIXX509Credential,
sec:MetadataPKIXSignature)

The sources to be looking at are down in org.opensaml.xmlsec.keyinfo....

R