I've tried to make Headlamp work with GKE/GDC clusters multiple times on macOS but I simply cannot get it working correctly w/gke-gcloud-auth-plugin. Worked out of the box with Luxury Yacht. I do also like the speed of Luxury Yacht!
Have you checked out headscale? It’s an open source control plane for Tailscale which lets you plug in any OIDC provider. Tailscale the company even employs an engineer which uses about 50% of his time on headscale.
There is an alternative ACME server implementation available from Buypass: https://www.buypass.no/ssl/products/acme. Haven't tried it personally, but they launched support for ACME v2 in late 2019.
I have a friend with a 13" MacBook Pro Retina (Early or Mid 2015) which this happened to. Nothing has ever been modified on that computer, hardware wise.