Using Auto-Increment value in MYSQL Before Insert Trigger?

PLEASE USE AFTER INSERT AND UPDATE

Do not make auto_increment any column you want to manipulate explicitly. That can confuse an engine and cause serious problems. If no column you have used for primary key are auto_increment you can do anything you want with them via triggers. Sure generated values will be rejected if they violate the mandatory uniqness of the primary key.

OP's comment:
How would I do it before, thou?

You can find current auto_increment value that is to be assigned to a new record.
And use the same in the before trigger as a parent user id for user_records table.
You have to query information_schema.tables table to find the value.

Example:

use `gknet`;

delimiter $$

drop trigger if exists before_create_user; $$

create definer=`root`@`localhost` trigger `before_create_user` 
       before insert on `users` 
for each row begin
  declare fk_parent_user_id int default 0;

  select auto_increment into fk_parent_user_id
    from information_schema.tables
   where table_name = 'users'
     and table_schema = database();

  insert into user_records ( action, userid, timestamp )
         values ( 'created', fk_parent_user_id, now() );
end;

$$

delimiter ;

Observations:
As per mysql documentation on last_insert_id(),

"if you insert multiple rows using a single INSERT statement, LAST_INSERT_ID() returns the value generated for the first inserted row only."

hence, depending on last_insert_id() and auto_increment field values in batch inserts seems not reliable.

Change the trigger to after insert instead of before insert and use NEW to get the last inserted id

USE `gknet`;
DELIMITER $$
CREATE DEFINER=`root`@`localhost` 
TRIGGER `after_create_user` AFTER INSERT ON `users` 
FOR EACH ROW 
BEGIN
INSERT INTO user_records (action, userid, timestamp)
  VALUES ('CREATED', NEW.ID, NOW() );
END; $$