/etc/maas/preseeds/enlist is in maas-region-api 2.4.0~beta2-6865-gec43e47e6-0ubuntu1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
| 1 2 3 4 5 6 7 8 9 10 | #cloud-config
datasource:
  MAAS:
    timeout : 50
    max_wait : 120
    # there are no default values for metadata_url or oauth credentials
    # If no credentials are present, non-authed attempts will be made.
    metadata_url: {{metadata_enlist_url}}
output: {all: '| tee -a /var/log/cloud-init-output.log'}
 |