It seems that I may have inadvertently loaded the password validation plugin in MySQL 5.7. This plugin seems to force all passwords to comply to certain rules.
CREATE USER 'username'@'localhost' IDENTIFIED BY 'password';
GRANT ALL PRIVILEGES ON *.* TO 'organizer'@'localhost' WITH GRANT OPTION;
CREATE USER 'username'@'%' IDENTIFIED BY 'password';
GRANT ALL PRIVILEGES ON *.* TO 'organizer'@'%' WITH GRANT OPTION;
FLUSH PRIVILEGES;