Jabber SDK via Expressway - NAT / Firewall Traversal

The CAXL JavaScript/XMPP/BOSH library has not been engineered to use Expressway, or otherwise to directly support firewall traversal.  Probably the official recommendation would be to use VPN, however as CAXL uses BOSH (based on HTTP)  you may be able to implement your own NAT traversal solution using standard tools (however Cisco does not provide any design guidance there.)

You may want to take a look at the Cisco Spark cloud-based chat (plus voice/video/meeting/etc.) platform, which provides easy to use client REST APIs for implementing chat regardless of network location.