I had the urgent need to configure some specific stuff in MySQL 5.7 on my developer machine, a MacBook Pro running Mac OS Sierra. Unfortunately, I did not find a my.cnf file that could be customized anywhere?
Internet research showed that MySQL Database Server on Mac OS runs without a my.cnf config file by default, simply started with default values.
Luckily, it is pretty simple to customize the MySQL Server installation by creating and editing a custom my.cnf file like this:
sudo cp /usr/local/mysql/support-files/my-default.cnf /etc/my.cnf
Then edit / customize the /etc/my.cnf file as required and restart your MySQL Server.