By default you can't access these headers as I know. What you can do is pass the httpresponse to a XML import mapping.
Because Mendix is not compatible with the AnyAttribute in schemas stated in the documentation (https://docs.mendix.com/refguide/xml-schema-support#1-introduction) which is used in the SOAP reference schema(https://schemas.xmlsoap.org/soap/envelope/) you need to create a specific one.
Hope this helps :)
cheers!