Add/User Delete activities

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Adds a Server class for processing server activities, such as Federating a delete_user action

Fixes #566 https://gdpr.eu/right-to-be-forgotten/

Proposed changes:

• Adds a Server class for processing server related activities
• Adds an activitypub_send_server_activity method for Server initiated activities
• Adds a delete_user action to Federate an actor Delete activity

Other information:

I've started this from @mattwiebe's Profile Update PR, so it makes sense for that to be merged 1st. I can rebase this later if needed

Followup PRs:

The Server class, and activitypub_send_server_activity will also be useful for Inbox forwarding activities (mainly Updates, Deletes)

• [ ] Have you written new tests for your changes, if applicable?

Testing instructions:

• Go to '..'

[pfefferle]

looks interesting

I think sooner or later we need an outbox when the number of outgoing activities steadily grows...

[Cambridgeport90]

Looks like this plugin’s really improving markedly since the last time I used it.

From: Matthias Pfefferle @.> Sent: Thursday, November 9, 2023 12:48 To: Automattic/wordpress-activitypub @.> Cc: Subscribed @.***> Subject: Re: [Automattic/wordpress-activitypub] Add/Server activities (PR #552)

looks interesting

I think sooner or later we need an outbox when the number of outgoing activities steadily grows...

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For now we're just deriving known Servers based on current users followers, I'll add the blog followers here as well.

But (in a subsequent PR) we'll have to think about tracking known users:

Receiving an actor Delete means we should delete any Comments they've sent. And possibly Inbox Forward the Delete Activity.

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@pfefferle after testing, the activity must be signed by the actor (mastodon ignores the actor Delete signed by the application actor).

Since the activity is scheduled, it creates a race condition where even if we pass the user_id to safe_remote_post the user is likely to be deleted by the time the signature is generated.

So a workaround would be to store key pair in an option during delete_user action and delete the option during deleted_user.

Code update forthcoming