Registering Rancher managed clusters in Argo CD doesn't work out of the box unless the Authorized Cluster Endpoint is used. Many users will prefer an integration of Argo CD via the central Rancher authentication proxy (which shares the network endpoint of the Rancher API/GUI). So let's find out why registering clusters via Rancher auth proxy fails and how to make it work.
Hint: If you are just looking for the solution scroll to the bottom of this page.