Distant notifications and user view permissions

The MR in djangoldp-account proposes that the user views including /users/xyz/inbox/ would require authentication (djangoldp-account!94 (closed))

Currently the notifications sent by this package are not authenticated

Solutions could be to authenticate it with the server key or with a user agent. It's a variation of the issue with Activity authentication:

• djangoldp#236
• djangoldp#372