Hi all.
I make a call to FS callcenter using webRTC. Now I would like to add some additional data to the header.
That I did by using extraheaders. Now all that is good. I can see the custom header in the sip trace on freeswitch.

For e.g in sip.js I add:

var options = {

extraHeaders: [ 'a: foo' ]

};

on FS i get:

INVITE sip:900@anonymous.invalid SIP/2.0

Via: SIP/2.0/WS 9jscv0q24s4m.invalid;branch=z9hG4bK1002472

Max-Forwards: 70

To: <sip:900@anonymous.invalid>

From: <sip:anonymous.hfsqa4@anonymous.invalid>;tag=depmif1fo5

Call-ID: l5pieavpjguoset7ugvd

CSeq: 1458 INVITE

a: foo

Contact: <sip:8rgi365g@9jscv0q24s4m.invalid;transport=ws;ob>

Allow: ACK,CANCEL,BYE,OPTIONS,INVITE,MESSAGE

Content-Type: application/sdp

Contact: <sip:8rgi365g@9jscv0q24s4m.invalid;transport=ws;ob>

Allow: ACK,CANCEL,BYE,OPTIONS,INVITE,MESSAGE

Content-Type: application/sdp

Supported: outbound

User-Agent: SIP.js/0.5.0

Content-Length: 3636

How do I access it in the dialplan? I tried ${sip_h_X-a} but it didnt't work. Help please?