Security

The website is served over an insecure connection and the plugin is offered as an insecure download. As a result, I haven't been able to test the web editor yet. Can you rectify those issues?

Hello,

The website is under https://create.arduino.cc you can directly download the agent from https://downloads.arduino.cc/CreateBridgeStable/ArduinoCreateAgent-1.1-windows-installer.exe or accordingly to your system as described here:
arduino-create-agent/README.md at main · arduino/arduino-create-agent · GitHub changing http to https.

The getting started guide is not under https only to protect your data (you are logged out then) and as soon as you installed the agent you switch back to https.
Https connection is mandatory in Arduino Create.