Messages are forwareded when received from another link, this means it's
too late to throw an error that bubbles up to the code trying to send
the incorrect message thus defeating the purpose of the validation.
Only the controller has access to the secret needed to sign user tokens
so it makes sense for the user signing code to live in the controller.
This saves about 20ms on the time ctl takes to start up due to lib no
longer needing to import jsonwebtoken.