opensaml2: XML signature wrapping attack

Juraj Somorovsky, Andreas Mayer, Meiko Jensen, Florian Kohlar, Marco Kampmann and Joerg Schwenk discovered that Shibboleth, a federated web single sign-on system is vulnerable to XML signature wrapping attacks. More details can be found in the Shibboleth advisory at http://shibboleth.internet2.edu/security-advisories.html.