How to make a Root to get access to the MariaDB server, trough a client app like MysqlWorkbench?
The answer to this question should help you out:

$ sudo mysql -u root

[mysql] use mysql;
[mysql] update user set plugin='' where User='root';
[mysql] flush privileges;


In short, the new version of MariaDB checks to see what the system user is and only allows the actual system user root to log in to the DB user root. Disabling all plugins disables that functionality.