The SOAP message processing in HydraExpress essentially ignores SOAP headers. They are placed on the rwsf::CallInfo instance to be retrieved by the user if needed, but otherwise they remain unparsed. The one exception to this rule is the mustUnderstand attribute. As required by the SOAP specification, HydraExpress detects this attribute, and also as required by the specification, message processing stops and HydraExpress returns an error indicating that it will not parse the SOAP header.