add individual pay-per-view events as a future possibility.

63.md

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+NIP-63
+======
+
+Relay-based Paywalls
+--------------------
+
+`draft` `optional`
+
+This NIP specifies how relays can support _paywalled content_. Well, "paywall" is a misnomer as this NIP doesn't imply payment necessarily, it's agnostic about that, so better call it **premium content**.
+
+The idea is that a _content-creator_ should be able to manage a list of _premium-reader_ who have access to their premium content, then choose some specific relays to publish their content based on their known support for this NIP.
+
+Relays that support this NIP (as they could indicate in their [NIP-11](11.md) responses) should receive the list of users and use it together with [NIP-42](42.md) authentication in order to decide what content will be readable by each requester.
+
+### Premium event
+
+Any event can be premium, all it needs is a [NIP-70](70.md) `["-"]` tag and another tag `["nip63"]` that clearly indicates its situation.
+
+Because normal relays won't care about these tags it's enough for the _content-creator_ to release the event to these relays in order to make it "public" to everybody.
+
+### Membership Event
+
+Membership events must be sent directly to the relays that will implement the paywall. By default relays should not serve these events to anyone, only to the _content-creator_ directly. Because of this, these lists can be kept reasonably private as long as the _content-creator_ is discreet in his publishing, but can also be made public by being published to other relays.
+
+The lists are constituted of one event for each _premium-reader_, and their removal/update must be done with a [NIP-09](09.md) deletion request.
+
+```yaml
+{
+  "kind": 1163,
+  "pubkey": "<content-creator>",
+  "tags": [
+    ["p", "<premium-reader>"]
+  ],
+  // ...other fields
+}
+```
+
+### Relay behavior
+
+A relay that implements this NIP should:
+
+- signal `63` in its `supported_nips` NIP-11 field;
+- accept `kind:1163` events and not serve them to anyone except to their creator;
+- accept deletion requests for such events;
+- accept premium events containing `["-"]` and `["nip63"]` tags only from their creator;
+- only serve the premium events to users that have a matching `kind:1163`;
+- serve an `AUTH` challenge to any client opening a connection immediately.
+
+### Client behavior
+
+A client doesn't have to do much in order to access premium content: if a client is already very liberal with its authentication policies it will automatically perform NIP-42 AUTH whenever it connects to the relay; otherwise it may want to check if such relay supports `63` before deciding.
+
+After that, any `REQ`s should include premium content automatically and transparently. This means that while constructiing a normal "following" feed a client will get the premium content automatically and place it in front of the user.
+
+A client may decide to display these events differently if they have the `["nip63"]` tag.
+
+### Announcement
+
+Optionally a _content-creator_ can announce that they have premium content available by publishing an event:
+
+```
+{
+  "kind": 10163,
+  "content": "<something about the premium content, the price and other stuff, optionally>",
+  "tags": [
+    ["url", "<payment-page-url>"]
+  ]
+}
+```
+
+Where `<payment-page-url>` is a normal webpage that may have anything in it. From there on, payments are handled off-protocol. The entity that handled the payment is expected to somehow modify the list of _premium-readers_ or enable the user to modify it later.
+
+#### Zap relationship
+
+This NIP is payment agnostic, but that doesn't mean one shouldn't use zaps or nutzaps for this. Clients or third-party services may offer a feature to read all zaps, compute their sums according to any criteria and use that information to modify the list of _premium-readers_.
+
+### Future additions
+
+- more private list membership: perhaps doing an HMAC with the public key of the reader and a key that is shared with the relays will be enough for this.
+- tiered membership: custom tiers for fine-grained content access control can be added by adding a tag like `["tier", "a"]` to the `kind:1163` event and using a `["nip63", "a"]` tag in the events, for example.
+- teaser events: perhaps a `["nip63", "", "-"]` (negative) tag could cause an event to be displayed only to those that do not have access to its premium counterpart, this would also be managed by the relay.
+- relays for premium content different from the outbox relays?
+- individual "pay-per-view" content.