SAML

http://xml.coverpages.org/WSS-SAMLProfileV15.pdf
Sender Vouches and Holder-of-Key:
http://java.sun.com/webservices/docs/1.6/tutorial/doc/XWS-SecuritySamples7.html
http://e-docs.bea.com/wls/docs90/webserv/sec_assert.html#1052527