CAS-1468: X509SubjectAlternativeNameUPNPrincipalResolver

Microsoft (and others) support the embedding of a UserPrincipalName object as a SubjectAlternateName extension within an X509 certificate, allowing properly-empowered certificates to be used for network logon (via SmartCards, or alternately by 'soft certs' in certain environments). An X509UserPrincipalNameResolver class would make the use of CAS as a web single sign on solution incredibly easy for AD domains with an existing PKI infrastructure.
http://docs.oracle.com/javase/7/docs/api/java/security/cert/X509Certificate.html#getSubjectAlternativeNames()