Message Signature Validation

[Pivotal Issue 78632442][1]

[1]: https://www.pivotaltracker.com/n/projects/1163646/stories/78632442
> With the separation of configuration between IdP and SP, they needed a shared identifier, hence the marker interface. 
Ah I see, it's used for type hinting? I would suggest naming it 'Configuration' then. Naming it "Certifiable" or CertificateAware confuses me, leads me to believe that I can rely on it having certificates.

> In any case, the question is: can indeed both SP and IdP configurations be given here, or is my hunch that only IdP configuration may be used correct (in which case I remove this interface and typehint against the IdP conf object).
Both may be given as an SP may send a signed AuthnRequest to an IdP that would need to be verified.

> The possible behavior that I wanted to expose is to expose distinct getters for the keys, certData and certificate values without having to rely on SSP dictated string keys that are not communicated anywhere, and which documentation I have not found yet (albeit I have hardly searched :tongue: )

That would be nice and might give it some purpose, though I would probably still put it on a concrete Configuration class. Or you will have lots of interfaces. Actually it seems like you are trying to use an interface like a trait? I wish we could use 5.4 :(.