Message Signature Validation

[Pivotal Issue 78632442][1]

[1]: https://www.pivotaltracker.com/n/projects/1163646/stories/78632442
Keep in mind that this is library development, not framework development. Only that what is required will be given as configuration. Personally I think configuration is a bad name all together as it is a DTO in the library scope, however I do want to convey the original purpose of the object and possibly provide an adapter for SSP if needed - i.e. not break too much with the original naming ;)
We need to use the now being added functionality, where we (as app) can indeed have both roles in multiple variants. 
However, contrary to the use of the ported functionality in SSP, we're going to use this _per request_ without relying on non-library responsibilities (e.g. loading of configuration). Since we can and indeed must fulfill the role as multiple SPs and multiple IdPs, the configuration handed to the lib will change per usage/call of the lib, and will be injected as required. As an aside, for instance the container will also be a custom implementation from outside of this lib (as that is not really library scope) that is going to be injected into the SingletonContainer. This really is going to be treated as library inside an application, used for its merits: (un-)marshaling of SAML messages, signing and signature verification and message verification.
Having these distinct classes allows fine-tuning of behavior later on, without having to break method signatures and cause a BC issue.