Note that can_join() is not remote-user safe.

src/channel.c

@@ -705,6 +705,7 @@ is_quieted(struct Channel *chptr, struct Client *who, struct membership *msptr,
  * input	- client to check, channel to check for, key
  * output	- reason for not being able to join, else 0
  * side effects -
+ * caveats      - this function should only be called on a local user.
  */
 int
 can_join(struct Client *source_p, struct Channel *chptr, char *key)