Jon Udell discusses the SOAPAction header and its uses for filtering SOAP requests through a firewall. The concept of the header is that the client making the SOAP Request, places a SOAPAction header in the HTTP request describing what it is they are going to be doing. For example what method they will be invoking. When I first read this a few years back it did send question marks buzzing up through my head, as you cant really on an external description of what is going to happen. Jon put's it great with his analogy of External Underwear:
Did the notion advanced in DevelopMentor's FAQ -- that SOAP packets would declare intent by publishing interface and method names in the HTTP header -- make sense? At the time it seemed reasonable to me. But now, I wonder if a SOAPaction policy isn't rather like the scene in Bananas where the newly-installed dictator declares that "everybody must wear their underwear on the outside, so we can check." The interfaces that a company chooses to expose to the world are, in the end, a policy that will or won't be enforced, regardless of the SOAP toolkits in use or the translations performed in a request pipeline. Enforcement will always require more than checking for underwear on the outside. [Jon's Radio]
Those of us who were writing perl CGI apps way back in the early days of the Web learnt that you can't rely on the format of a request. You really do need to verify all data before you make any assumptions about it, so a http SOAPAction header specifying a Stock ticker lookup interface, can just as easily have a Stock trading message within.
All of this discussion though assumes that you only have one single SOAP gateway/router on your web server. This strikes me as a bit naive from a security standpoint. I think that only interfaces with the EXACT same security properties should be exposed in the same router. This way you can use the underlying web servers security as well as external firewall's to provide access control and authentication. Lets not reinvent the wheel here.
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