Message Signature Validation

[Pivotal Issue 78632442][1]

[1]: https://www.pivotaltracker.com/n/projects/1163646/stories/78632442
One problem we have had at OpenConext is that we enter the certData in Janus and sometimes it gets borked (when someone accidentally deletes a character or something. The structure is fine, but it just isn't a valid DER encoded certificate. That's why in our implementation we rely on openssl_x509_read to parser the certificate for us as it knows a bunch more about certificates.
Worth considering.