This is going to be a quicky, but since I just farted around for a couple of hours trying to figure it out-- led astray by our friend, AI, and then old SO posts-- I thought I'd record what turned out to be the answer for me:
I'm not going to explain much here... but...
I assume if you found this, you know what Kubernetes does, and you know what Keycloak does, and you're just wasting your precious life guessing at the secret. Well, friends, your ol' Uncle Rian is here for you.
It's just an environment variable.
Assuming you've got a pretty vanilla Kubernetes installation-- mine is microK8s on Ubuntu, but I get the feeling that this is a Keycloak v26 thing more than a particular k8s thing:
Do this:
- name: KC_PROXY_HEADERS
value: "xforwarded"
In your deployment env vars section.
I'd say let me know how it goes, but I don't have commenting enable at the moment