Here is the relevant section:
[sharing]
type = csv
database_path = /var/lib/radicale/collections/sharing.csv
collection_by_map = true
permit_create_map = true
Just FYI, my filesystem_folder is defined as /var/lib/radicale/collections.
BTW. The token based sharing, as I understand, still requires auth, just not an user auth but, well, a token one.