Native support for WS-Security was not added until IS 7.x. However, since a WS-Security token is just XML you can certainly chose a security token type, build the document types to support it, populate it and add it to the header of your outbound soap request.
Check out the “sticky” posts in this forum for ideas.
IS 6.1 is very, very old and no longer supported. You should consider upgrading to a newer version.
Mark
#webMethods#API-Management#soa