From the OpenSAML Wiki:
If your primary site was JSP (like Tomcat) or a Java application server (like Websphere or JBoss), then Java would be an obvious choice. Just as C# would be an obvious choice if you had a Microsoft/IIS server.
But since you're doing this in PHP (presumably on Apache), I'm thinking maybe the C++ OpenSAML library might be better (although Java would probably be acceptable).
You can download the libraries and documentation, or join the OpenSAML community, here:
'Hope that helps!