Applied SOAP: Implementing .NET XML Web Services

The SOAP Header

Because the SOAP Header is an optional object, you might or might not find header information serialized in a given SOAP packet. But if there is header information, all of that information must be serialized within the SOAP Header object, which must be the first (XML) child of the Envelope element. That's where you'll find it, but what is it used for?

Well, in a nutshell, the SOAP Header is used to transmit auxiliary information relevant to the Web Service processing that isn't part of the method signature. For example, imagine that you have a Web Service that specifies the toppings and crust style of the pizza that you intend to order (in C#):

OrderInfo OrderPizza(int[] toppings, int[] crust, PaymentInfo pi);

For this example, ...