Following activities

[jg10-mastodon-social]

Following activities from an actor can be performed by sending a Follow request and then processing resources that have been POSTed to the inbox with public append permissions.

Processing can be performed by an agent that has access to the inbox LDP container.

• Sending activities #14
• Actors' inbox and outbox #7

Example

• https://browser.pod-os.org/?uri=https%3A%2F%2Fjg10.solidcommunity.net%2Fdevlog%2Ffollowing%2520activities.md

[jg10-mastodon-social]

I can also now confirm that the agent processing the inbox can do so by subscribing to a WebhookChannel2023. The webhook requests are authenticated by a notifications webid owned by the resource server, which the agent can authorise (in addition to verifying the ActivityPub message itself).

Anything that can be done at a custom inbox endpoint can therefore be done by the agent instead, albeit asynchronously.

The main advantage of this architecture is that it maintains separation of data at rest - provided by the resource server - and custom server-side operations - provided by the agent.
An agent can service many resource servers without changes to the Solid specs, and if the agent doesn't store any data, it can also be implemented as a serverless function.

The architecture I have experimented with avoids storing data by appending to the latest page of the inbox collection. My webhook server is still storing dpop jti to avoid replay of notifications. I'm not sure how to avoid that (other than by removing this protection).

[jg10-mastodon-social]

ActivityPub-interoperable subscription is described in https://www.w3.org/TR/social-web-protocols/#subscribing-with-follow

An ActivityPub inbox is actually a constrained version of a LDN inbox: https://www.w3.org/TR/social-web-protocols/#delivery-activities