Set up HTTP authentication as taught in the CGI programming course (there is a ready-made password file in /etc/apache/training.passwd) and use it to protect the whole Acme Widget Co. site.
Alter the tables in your database using the SQL alter statement to give them fields for the user who altered records and the date and time they were altered. The documentation for this SQL statement is available in the MySQL manual.
Record each transaction's timestamp and the user who made the transaction. Use the REMOTE_USER environment variable to find the username.