Support for SIP (Subscribe/Notify) in standard http nodes

I would like to use the Session Initiated Protocol source with standard Node-RED http nodes.

A user agent interested in event notification sends a SUBSCRIBE message to an SIP server. The SUBSCRIBE message establishes a dialog and is immediately followed by the server replying with 200 OK response. At this point the dialog is established. The server sends a NOTIFY request to the user every time the event to which the user subscribed changes. NOTIFY messages are sent within the dialog established by the SUBSCRIBE.

More information

For that I need 2 things:

  1. http - in node: Supporting method "NOTIFY"
  2. http - request node: Supporting "SUBSCRIBE" / "UNSUBSCRIBE"

Topic 2. does already work when using - set by msg.method - in spite of documentation saying that only the value put, get, etc are allowed.