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89 lines
3.6 KiB
Markdown
89 lines
3.6 KiB
Markdown
NIP-42
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======
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Authentication of clients to relays
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-----------------------------------
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`draft` `optional` `author:Semisol` `author:fiatjaf`
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This NIP defines a way for clients to authenticate to relays by signing an ephemeral event.
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## Motivation
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A relay may want to require clients to authenticate to access restricted resources. For example,
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- A relay may request payment or other forms of whitelisting to publish events -- this can naïvely be achieved by limiting publication
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to events signed by the whitelisted key, but with this NIP they may choose to accept any events as long as they are published from an
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authenticated user;
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- A relay may limit access to `kind: 4` DMs to only the parties involved in the chat exchange, and for that it may require authentication
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before clients can query for that kind.
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- A relay may limit subscriptions of any kind to paying users or users whitelisted through any other means, and require authentication.
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## Definitions
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This NIP defines a new message, `AUTH`, which relays can send when they support authentication and clients can send to relays when they want
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to authenticate. When sent by relays, the message is of the following form:
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```
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["AUTH", <challenge-string>]
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```
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And, when sent by clients, of the following form:
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```
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["AUTH", <signed-event-json>]
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```
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The signed event is an ephemeral event not meant to be published or queried, it must be of `kind: 22242` and it should have at least two tags,
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one for the relay URL and one for the challenge string as received from the relay.
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Relays MUST exclude `kind: 22242` events from being broadcasted to any client.
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`created_at` should be the current time. Example:
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```json
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{
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"id": "...",
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"pubkey": "...",
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"created_at": 1669695536,
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"kind": 22242,
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"tags": [
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["relay", "wss://relay.example.com/"],
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["challenge", "challengestringhere"]
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],
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"content": "",
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"sig": "..."
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}
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```
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## Protocol flow
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At any moment the relay may send an `AUTH` message to the client containing a challenge. After receiving that the client may decide to
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authenticate itself or not. The challenge is expected to be valid for the duration of the connection or until a next challenge is sent by
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the relay.
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The client may send an auth message right before performing an action for which it knows authentication will be required -- for example, right
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before requesting `kind: 4` chat messages --, or it may do right on connection start or at some other moment it deems best. The authentication
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is expected to last for the duration of the WebSocket connection.
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Upon receiving a message from an unauthenticated user it can't fulfill without authentication, a relay may choose to notify the client. For
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that it can use a `NOTICE` or `OK` message with a standard prefix `"restricted: "` that is readable both by humans and machines, for example:
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```
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["NOTICE", "restricted: we can't serve DMs to unauthenticated users, does your client implement NIP-42?"]
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```
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or it can return an `OK` message noting the reason an event was not written using the same prefix:
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```
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["OK", <event-id>, false, "restricted: we do not accept events from unauthenticated users, please sign up at https://example.com/"]
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```
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## Signed Event Verification
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To verify `AUTH` messages, relays must ensure:
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- that the `kind` is `22242`;
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- that the event `created_at` is close (e.g. within ~10 minutes) of the current time;
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- that the `"challenge"` tag matches the challenge sent before;
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- that the `"relay"` tag matches the relay URL:
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- URL normalization techniques can be applied. For most cases just checking if the domain name is correct should be enough.
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