Feature/673 xauth token

### Description
X-Auth-Token forwarded in notifications

Implements #673 
Maybe we should include the following:

"//FIXME: note that the X-Auth-Token is left blank in this case. In the future, maybe the ONTIMEINTERVAL notification struture could include it (and a TRUST_TOKEN to re-negotiate X-Auth-Token if it gets expired)"

or something like that.