How to create digital signature when invoking Webservice sec

Hi folks,
using ABL we want to invoke webservice operation secured by WS-Security standard. That means we need to put digital signature inside SOAP request. Did anyone solve similar usecase?

Since WS-Security is not implemented in 11.6 we decided to create the signature out of OpenEdge using .NET external call. As defined in WS-Security the signature should be stored in SOAP header which is feasible with current OpenEdge API (SOAP header callback).

Now the problem:
To create the signature we need the whole SOAP body XML in the same form as it will be sent out. Anyone knows how to get to access the SOAP body xml. We didn't find any clue for this in DOC.

Regards,

Jan