A simple way, to exchange data, allows the following nginx configuration. Files can be uploaded (and overwritten) via a WebDAV put interface, and downloaded by using get requests. Any actions require the input of basic auth credentials for security reasons. The configuration is a single user mode, so even if multiple basic auth credentials are stored, the same files are visible to each user.
If no htpasswd file exists yet, it can be created with the following command:
# htpasswd comes from apache2-utils, install it using:
apt install apache2-utils