It seems I may have left out an important piece of information regarding configuring the controller. I assumed the default authentifcation method was 'None', when it may actually be 'Password'.
If you want to start a controller without password authentification, you need to edit the controller configuration file, which is
/Library/Preferences/com.apple.xgrid.controller.plist. Change the authentication method to
None, and then restart the controller with the command
sudo xgridctl c restart (or
start if it is not running).