how can a payment processor automatically modify the list of authorized readers if it doesn't have the creator keys?
Discussion
Well, it cant, but a service could receive a bunkerlink from the creator, where the creators bunker/remote signer only allows for the automatic signage of such lists events
I can imagine many more models, but there are three elements:
The required action infrastructure (for instance creditcard payments);
The observation the action occured (for instance the payment provider anouncing a payment happened via a DM);
The mutation of the list (for example a bot on the creator side that looks for such dm's before it takes action).
The last part always demands something from the content creator because of requirement to sign with particular keys, but where those other two are residing could differ.
The creator is authorizing the relay to act on (or not) whatever particular information it receives, in order to serve content, so it's just collecting data until it meets a certain threshold. Starting out, that's zap reciepts.
A (possibily close) future implementation could be that the creator tells their WoT provider that they want to send "premium" notes to only their most trusted associations. That provider could collect mutual interactions or whatever until they meet some defined threshold. At which point, that provider could send the newly approved npub to the relay, and the relay can start acting. The lockbox relay is kind of a light version of that now, serving notes to only the author's follow list.
Integrating traditional payment methods could be a simple form with CC info with a spot for an npub. A relay would just need to be modified to listen for said information and the payment processor would just need to send the proof of payment + npub.