AS4 18.104.22.168 and 22.214.171.124 require support for PMode.Security.X509.Sign in ebHandler.
This parameter is defined in the core specification as:
The value of this parameter is a list of the names of XML elements (inside the SOAP envelope) that should be signed, as well as whether or not attachments should also be signed. The list is represented in two sublists that extend this parameter: Sign.Element and Sign.Attachment. An element within the Element list could be specified either by its XML name or by its qualified name (its XML name and the namespace to which it belongs). An element within the Attachment list is identified by the Content-Id.
However, AS4 sections 5.1.4 and 5.1.5 are clear about what is to be signed in an AS4 message. So having the ability to explicitly select parts to sign is unnecessary and could lead accidental misconfiguration.