Signature validation filter config

[Rod Widdowson]

> >1) The default value for 'requireSignedMetadata' in V2 was FALSE.
> 
> I think you mean requireValidMetadata.

No  I really do mean "requireSignedMetadata".  It's an attribute inside
xsi:type="sec: SignatureValidation".  If it is not specified (or defined to
be false) then the SignatureValidationFilter will not complain if the
supplied metadata doesn't have a signature.  With it true
SignatureValidationFilter complains if the signature fails or if there is no
signature.  My feeling is that having the default be false opens up to an
attack in which unsigned metadata is provided as a replacement to signed
metadata.
 
> I'm fine with a subset, but I probably would like to see both cert and
> public key supported, just because it's gratuitous to even require a cert
> there.

Good point.   I'll see about adding both.

Thanks