RE: [security-services] Authentication Method

> Liberty stipulated that the saml:AuthenticationMethod would logically
> indicate 'see Authentication Context' with a value of
> 'urn:liberty:ac:2003-08.'

I left this in (with a modified URI) when I added AuthnContext to core, but
I think there's an overlap to examine between AuthenticationMethod and
AuthnContextClassRef. Seems to me that both could be read as constraining
the set of context statements one might be dealing with.

-- Scott