Arnon cites his paper which builds on Deutsch, Gosling and Joy's famous Fallacies of Distributed Computing, specifically Fallacy #4 "the network is secure" These are common mistakes people make when building disiributed apps. Arnon blogged this:
This is a great way to think about the problem, and as Arnon says its not just an issue with SOA security, its a pervasive issue. If you think REST+SSL is a security architecture then you should consider what threats you are choosing *not* to deal with.In my opinion, assuming the network is secure for an SOA is not only naïve but negligence pure and simple. The whole premise of moving an organization to SOA is connectedness and integration. So, unless your SOA will fail it will be connected to other systems. Whether you are building RESTful systems, WS-* SOAs, EDAs or any combination of these architectural styles, If you won’t treat the services boundary as a border and secure it – you will be sorry…
Security in SOA should be considered at the "grand-scheme" level with issues like authertication, authorization but also at the single service level, looking at issues like DDOS, SQL injection, elevation of privilige and what not. A trivial thing like exposing a transaction beyond service boundaries can translate to an attacker denying services in your system simply by locking out your database. Again, this is just a simple example.
The other thing about Security is that you have to consider it early. patching security "later on" can have devestating effects on a system's capabilites esp. in areas related to performance. I have seen even military systems that had to go through serious rework, just because Security was added as an afterthought instead of handled early on
