src/arm-ubuntu/disk-image/arm-ubuntu/cloud.txt

#cloud-config
users:
  - name: ### insert the username here ###
    ssh-authorized-keys:
      - ssh-rsa ### insert the rsa key here ###
    sudo: ['ALL=(ALL) NOPASSWD:ALL']
    groups: sudo
    shell: /bin/bash
    homedir: ### insert the home directory here ###