I'd like my JSON:API responses to return the e-tag header so that consuming remote sites can determine (e.g. with a HEAD request) if they need to ditch their cached responses and re-fetch. There is no last-modified or e-tag headers being sent at all - for any Drupal page for that matter. How can I enable this? Thanks!
I do see
X-Drupal-Cache headers, but this isn't enough to go on.
Running Drupal 8.6.10 and JSON:API 8.x-2.4.