Rancher on k3s cluster initial login failed

I have set up a rancher 2.4.6 on a k3s cluster on two virtual machines. In front I configured an apache reverse proxy on the host of the VMs. All status kubectl commands tell me that everything is fine, I have a running ingress on the cluster:
# kubectl get ingress -n cattle-system
rancher rancher.zuhause.xx 80, 443 2d6h

When I try to access my rancher ui, I see

From earlier installations on docker I would have expected to set an initial password on the login screen, however user admin with default password does not lead to a login, it shows only for 2 sec logging in and nothing happens. The logs on the reverse proxy indicate that there is an authentication problem - - [23/Sep/2020:22:14:48 +0200] “GET /v3/users?me=true HTTP/1.1” 401 436 “https://cranran.zuhause.xx/login
I would be very grateful for any advice how to dig into this further …
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