users.yml

id: users
label: User migration
migration_tags:
  - Drupal 6
  - Drupal 7
source:
  plugin: d6_user
process:
  # If the entity's ID is migrated, the Migrate API will try to update
  # an existing entity with that ID. If no entity with that ID already
  # exists, it will be created.
  uid: uid
  name: name
  mail: mail
  password: password
  'signature/value':
    plugin: default_value
    default_value: 'The answer is 42.'
destination:
  plugin: entity:user
  # If the destination is going to update an existing user, you can optionally
  # specify the properties that should be overwritten. For example, if the
  # migration tries to import user 31 and user 31 already exists in the
  # destination database, only the 'name' and 'mail' properties of the user
  # will be overwritten. If user 31 doesn't exist, it will be created and
  # the overwrite_properties list will be ignored.
  overwrite_properties:
    - name
    - mail
    # It's possible to overwrite nested properties too.
    - 'signature/value'