First of all, we need to set root password as default one is username root with no password.
Then run cli, then switch into configuration mode with: configure
And apply following command:
set system root-authentication plain-text-password
You will be asked to provide password and password confirmation.
Then you need to apply change using commit command.
After that enable ssh:
set system services ssh
And enable root login over ssh (not recommended for production use):
set system service ssh root-login allow
And finally apply all changes using commit command.
