clarify `created_at` and auth session duration.

42.md

@@ -43,7 +43,8 @@ WebSocket URL of the relay. `created_at` should be the current time. Example:
 ```
 
 The client may send an auth message right before performing an action for which it knows authentication will be required -- for example, right
-before requesting `kind: 4` chat messages --, or it may do right on connection start or at some other moment it deems best.
+before requesting `kind: 4` chat messages --, or it may do right on connection start or at some other moment it deems best. The authentication
+is expected to last for the duration of the WebSocket connection.
 
 Upon receiving a message from an unauthenticated user it can't fulfill without authentication, a relay may choose to notify the client. For
 that it can use a `NOTICE` message with a standard prefix `"restricted: "` that is readable both by humans and machines, for example:
@@ -62,7 +63,7 @@ or it can return an `OK` message noting the reason an event was not written usin
 
 To verify `AUTH` messages, relays must ensure:
 
-  - that the `kind` is `22242`
-  - that the event was recently signed (~10 minutes, by `created_at`)
-  - that the `content` field matches the relay URL
+  - that the `kind` is `22242`;
+  - that the event `created_at` is close (e.g. within ~10 minutes) of the current time;
+  - that the `content` field matches the relay URL:
     - URL normalization techniques can be applied. For most cases just checking if the domain name is correct should be enough.