Users are authenticated by mod_auth_kerb which works great. Therefore I need to set
If there is no valid user Apache fails with an 401 Authorization Required. I would like Apache to deliver the website anyway but without providing a
REMOTE_USER to the underlying application (python code, or php script).
This is related to How to tell mod_auth_kerb to do its job despite no "require valid-user". But with the important difference that on a whole sub directory on every URL a Kerberos negotiation should be initiated, and if it fails it should deliver the content anyway.