Farcaster client applications can host mini apps. Allowing those mini apps to push notifications to users requires the host to generate user notifcation tokens, send signed messages to the mini-apps webhook, and accept notifications via webhook. Neynar provides a system to manage this complexity on behalf of the client app (mini app host).
An event sent to a mini-app webhook must be a signed JFS messages. There are two supported signing approaches in this system. Hostcaster can sign the message with a user’s key if they have the ability to do so. Or, if Hostcaster instead uses the Neynar-hosted signer system then they can provide their signer_uuid when posting the unsigned event.
GET /v2/farcaster/app_host/user/event to retrieve the message to be signed. This is particularly important for notification_enabled events because this is when a notification token is generated by Neynar
Sign the message, serialize the entire bundle per JFS spec