If you tab through the Juniper CLI attempting to add a user you will ultimately end up typing the following which after pressing enter will prompt you for the password two times.
set system login user bob authentication plain-text-passwordThis isn’t very easy to automate and cannot be copy and pasted into the configuration. Juniper has a hidden command ‘plain-test-password-value’ which can be used for this.
set system login user bob authentication plain-text-password-value password123
Work, and stuff 