You can use the platform.session,session_token provided you are logged in. I have done a simple test to dump the platform and event objects in the user.session post event and they return null which means you are in fact not logged in (yet) during a user/session post event. Any other post event after session, you’re probably fine. But in this case I think it’s a chicken/egg thing:
var_dump(event) returned:
[27-Feb-2016 16:24:30 UTC] REST Exception #404 > Could not find a service for dreamfactory
and var_dump(platform) returned:
[27-Feb-2016 15:40:11 UTC] REST Exception #400 > Bad request. No token or api key provided.
If you are attempting to append a param to the session response, you will need to log in first (get a session then pass session and api_key to your table call. But since the session you want to modify doesn’t exist during the event, i’m not sure how you would extend it. Good question though (if it’s even possible). I’ve found nothing else on how to do this. Knowing this, I would append the session var after login in a separate call.
As for logging and debugging:
From your dreamfactory install folder to can tail storage/logs/dreamfactory.log. On Bitnami Windows for example its:
C:\Bitnami\dreamfactory-2.1.0-4\apps\dreamfactory\htdocs\storage\logs\dreamfactory.log
var_dumps and errors typically are logged in dreamfactory.log (unless you have significantly customized your install). While debugging i would var_dump and not throw until you are sure you are retrieving what you want, and check the log. That is my preference as I have seen that using throw interferes with var_dumps or debugging output in the log (probably due to event propagation between v8js and php). A DF engineer may have more clarification on this.
Instead of throwing, do this to see what your venue.content.resource is returning (assuming you are logged in):
var_dump(venue.content.resource);
If you don’t see values in your array in the log, that would be the reason for your error.
Hope this helps.