mysqldump --opt --credfile /etc/mysql_creds mydatabase > output.sql

username=myuser
password=ToPsEcReT

$ mysqldump --defaults-extra-file=mycred.cnf ...

$ cat mycred.cnf
[mysqldump]
user = myuser
password = xyzzy

$ mysql_config_editor set --login-path=dump --host=localhost --user=root --password
Enter password:

$ mysqldump --login-path=dump ...