Serve webdav Dir.ReadDirAll error

Nice one - that is exactly what the AUTH proxy is for.

You are configuring a webdav remote in the output of the auth proxy but you haven't set the "url" parameter

So you need to add

{
    "type":"webdav",
    "url": "https://wherever",
...

}

Note that host isn't a parameter for the webdav backend.