Have you ever tried to study SOA Security? It is kind of time taking and a bit of complex job. It contains a huge stack of standards like WS Security, WS Security Policy, WS Trust, WS Username Token Profile, SAML, and many more down the line, and a lot of new buzz words, terminology. You might have gone through each of these documents, spent hours in finding the relationship among them. It needs days of brainstorming and lot of hands on experience, believe me..
But this is the best point to start learning SOA Security, build the big picture, and then go into deep. This presentation by Prabath Siriwardena, who leads the WSO2 Security Team touches all the corners of SOA Security in a brain friendly manner. He has adopted a Head First * like style in presenting the concepts.
If you are into SOA, definitely it is worth going through this. It won't take much time, but it will ended up giving you the essense of SOA Security.