Please, consider adding preemptive authentication for Deluge. I'm using a reverse proxy in combination with Authelia multi factor authentication portal (https://github.com/clems4ever/authelia) and I can't connect to Deluge at the moment because of this missing feature.
In case you were wondering, Sonarr and Radarr are working correctly, because as I can see from my server's logs they send the authentication header with every request, even the first one.