[Users] How to test for domain in sip request in openser.cfg.

Hello, I would like to test for the domain name in a sip request to decide if an invite is accepted or not. I have the following lines in my openser.cfg file to cater for DNS SRV forwarding: # accept calls from foo.com if ( is_method("INVITE") ) { rewritehost ("sipproxy.foo2.com"); rewriteport (""); } This works well, but I would like to tighten security by only allowing invites forwarded by foo.com. When debugging using xlog calls, the pseudo-variable I am after is : $rd. However $rd can not be used in openser.cfg as follows: if ( is_method("INVITE") && $rd="foo.com" ) Documentation suggests to use core keywords like: if(is_method("INVITE") && from_uri=~".*(a)foo.com") This does not work for my situation and I don't know how I can see the value of 'from_uri', as it can't be expanded into xlog calls. So my kind of overlapping questions are: How can I use pseudo-variables in openser.cfg to test for a certain value? How can I see (debug) the contents of a core keyword? Which keyword should I be using to solve this issue? Has anyone solved a similar issue in the past and if so can you please give some details? Thanks, Bas.