Where store password / login-path in MariaDB (equivalent for mysql-config-editor)?

You can use an unencrypted options file. Create a new options file in your home directory, readable only by you, like this:

[client]
host='<your-db-host>'
port='<your-db-port>'
socket='<your-db-socket>'
database='<your-db-name>'
user='<your-db-user>'
password='<your-db-password>'

You can then use with a --defaults-extra-file= option when running one of the clients.

Configuring MariaDB with Option Files

You can create different config files for each login path you would have created.

The MariaDB team are taking the position that the obfuscated file is providing only a false sense of security so you're better off just facing up to the fact that you're placing your password in your filesystem in plaintext. If you have your file permissions configured correctly this can be an acceptable situation.