I am using a JSSIP client and they claim to be implemented RFC-5626.
Following are  the REGISTER and response messages. Is it possible to confirm the JSSIP client has full implementation of SIP outbound?
If it supports fully then I can debug outbound and gruu functionality at Kamailio(I have it enabled but it didn't work, have to see if I need to enable any more settings).
 
REGISTER sip:sip.engageio.com SIP/2.0
Via: SIP/2.0/WSS 5qfe1k7uvuaf.invalid;branch=z9hG4bK563864
Max-Forwards: 69
To: <sip:123456543_28iseh@sip.engageio.com>
From: "123456543" <sip:123456543_28iseh@sip.engageio.com>;tag=em9kvbdqg2
Call-ID: 071s1uno9bk7ie1hf0p3dn
CSeq: 1 REGISTER
Contact: <sip:h0pg4fas@5qfe1k7uvuaf.invalid;transport=ws>;+sip.ice;reg-id=1;+sip.instance="<urn:uuid:b7d40d83-b1f4-4419-bced-4c464507dea6>";expires=600
Expires: 600
Allow: INVITE,ACK,CANCEL,BYE,UPDATE,MESSAGE,OPTIONS,REFER,INFO,NOTIFY
Supported: path,gruu,outbound
User-Agent: JsSIP 3.7.5
Content-Length: 0


SIP/2.0 200 OK
Via: SIP/2.0/WSS 5qfe1k7uvuaf.invalid;branch=z9hG4bK563864;received=172.27.6.98
To: <sip:123456543_28iseh@sip.engageio.com>;tag=211517f31d5fe3f765e28c150e460fc3.0b7e0000
From: "123456543" <sip:123456543_28iseh@sip.engageio.com>;tag=em9kvbdqg2
Call-ID: 071s1uno9bk7ie1hf0p3dn
CSeq: 1 REGISTER
Contact: <sip:h0pg4fas@5qfe1k7uvuaf.invalid;transport=ws>;expires=600;pub-gruu="sip:123456543_28iseh@sip.engageio.com;gr=urn:uuid:b7d40d83-b1f4-4419-bced-4c464507dea6";temp-gruu="sip:uloc-60dc6c8a-7464-1-2dfe734@sip.engageio.com;gr";+sip.instance="<urn:uuid:b7d40d83-b1f4-4419-bced-4c464507dea6>";reg-id=1
Require: outbound
Supported: outbound
Server: kamailio (5.3.2 (x86_64/linux))
Content-Length: 0