AUTH doc updated for ACL.

Author: antirez

commands/acl-whoami.md

@@ -0,0 +1,14 @@
+Return the username the current connection is authenticated with.
+New connections are authenticated with the "default" user. They
+can change user using `AUTH`.
+
+@return
+
+@bulk-string-reply: the username of the current connection.
+
+@examples
+
+```
+> ACL WHOAMI
+"default"
+```

commands/auth.md

@@ -1,16 +1,36 @@
-Request for authentication in a password-protected Redis server.
-Redis can be instructed to require a password before allowing clients to execute
-commands.
-This is done using the `requirepass` directive in the configuration file.
+The AUTH command authenticates the current connection in two cases:
 
-If `password` matches the password in the configuration file, the server replies
-with the `OK` status code and starts accepting commands.
+1. If the Redis server is password protected via the `requirepass` option.
+2. If a Redis 6.0 instance, or greater, is using the [Redis ACL system](/topics/acl).
+
+Redis versions prior of Redis 6 were only able to understand the one argument
+version of the command:
+
+    AUTH <password>
+
+This form just authenticates against the password set with `requirepass`.
+In this configuration Redis will deny any command executed by the just
+connected clients, unless the connection gets authenticated via `AUTH`.
+
+If the password provided via AUTH matches the password in the configuration file, the server replies with the `OK` status code and starts accepting commands.
 Otherwise, an error is returned and the clients needs to try a new password.
 
-**Note**: because of the high performance nature of Redis, it is possible to try
+When Redis ACLs are used, the command should be given in an extended way:
+
+    AUTH <username> <password>
+
+In order to authenticate the current connection with one of the connections
+defined in the ACL list (see `ACL SETUSER`) and the offical [ACL guide](/topics/acl) for more information.
+
+When ACLs are used, the single argument form of the command, where only the password is specified, assumes that the implicit username is "default".
+
+## Security notice
+
+Because of the high performance nature of Redis, it is possible to try
 a lot of passwords in parallel in very short time, so make sure to generate a
 strong and very long password so that this attack is infeasible.
+A good way to generate strong passwords is via the `ACL GENPASS` command.
 
 @return
 
-@simple-string-reply
+@simple-string-reply or an error if the password, or username/password pair, is invalid.