When receiving an ActivityPub Follow, send back an Accept activity
automatically. Due to application hook needed to fetch sending
user private key (for signing), this is only available if Django
is installed since currently application hooks exist only for
Django configuration.
Django applications should include a new configuration item
"get_private_key_function" which points to a function which takes
a user identifier (fid, handle or guid) and returns a private key
in RSA object format.
Allow enabling by setting the FEDERATION "activitypub" key to True.
This is done to not break compatibility for new users for
platforms which prefer activitypub.
Alain St-Denis