Somewhat related: If activity handler can reject activity based on some condition, this condition should be represented at the protocol level.
For example, if the server automatically rejects follow requests that don’t contain some kind of proof to reduce spam, the actor object may indicate this in the following way:
{
"id": "https://example.com/users/alice",
"type": "Person",
"canFollow": {
"type": "ProofOfX",
"description": "Do X before following me"
}
}
FEP-5624 describes something similar for replies, but it is very limited because the proposed canReply property simply lists actors who can reply. A proper solution should be compatible with all kinds of locks and approval mechanisms.
I guess this is the area where object capabilities would be actually useful.