Terminate the call if 200/OK response to INVITE to SIPS target is not secure

[bennylp]

The standard says that a SIPS dialog should be secure end to end. However some proxies or UASes disobey this requirement and give back plain SIP URI in the Record-Route or Contact header. We should terminate such call.

This ticket will implement Contact/Record-Route header checks in incoming initial/subsequent INVITE/UPDATE request or 2xx response to INVITE/UPDATE. Contact URI should use "sips" scheme and Record-Route URI should use either "sips" scheme or "transport=tls" param. As UAC, if it receives 200/OK response to initial/subsequent INVITE/UPDATE with insecure Contact/Record-Route, it will terminate the session. As UAS, if it receives initial/subsequent INVITE/UPDATE request with insecure Contact/Route headers, it will send response with SIP status code 480 and Warning header: 381 "SIPS required".

This feature can be disabled by setting pjsip_cfg()->endpt.disable_secure_dlg_check to PJ_TRUE (default is PJ_FALSE).

Here are some texts from the standard:

• All hops must use TLS (should we check if all Record-Route URIs use "sips" scheme or "transport=tls" param? Currently we'll just check the top Record-Route header)
  • ​http://tools.ietf.org/html/rfc5630#section-4:

    This document specifies that SIPS means that the SIP resource
    designated by the target SIPS URI is to be contacted securely, using
    TLS on each hop between the UAC and the remote UAS (as opposed to
    only to the proxy responsible for the target domain of the Request-
    URI).
    

• Contact header must use "sips" scheme:
  • in request ​http://tools.ietf.org/html/rfc5630#section-5.1.1:

    As mandated by [RFC3261], Section 8.1.1.8, in a request, "if the
    Request-URI or top Route header field value contains a SIPS URI, the
    Contact header field MUST contain a SIPS URI as well".
    

  • in target refresh ​http://tools.ietf.org/html/rfc5630#section-5.1.1.2:

    When a target refresh occurs within a dialog (e.g., re-INVITE
    request, UPDATE request), the UAC MUST include a Contact header field
    with a SIPS URI if the original request used a SIPS Request-URI.
    

  • in response ​http://tools.ietf.org/html/rfc3261#section-12.1.1:

    If the request that initiated the dialog contained a SIPS URI in
    the Request-URI or in the top Record-Route header field value, if
    there was any, or the Contact header field if there was no Record-
    Route header field, the Contact header field in the response MUST
    be a SIPS URI.