I've made some small progress today, thanks again to @bikesquid for your help with this. I am still having some issues with getting accurate status information, but thought it was a good time to open it up to anyone else who may want to test. This is by no means a functional driver, purely to test authentication and my interpretation of the data coming back.
Driver and Device Setup
The driver is still available at the same location, if you need a hand installing this please let me know.
https://raw.githubusercontent.com/sburke781/hubitat/KumoCloud_AuthPOC/KumoCloud_ParentDriverPOC.groovy
If you've still got a device setup from previous testing, I think you should be able to just update the driver code from GitHub and then test. If you haven't got a device setup, install the driver then setup a new Virtual Device referencing the driver. On the device edit page for the new Virtual Device, make sure you enter your user name and password and turn on the debug logging Preference, then click Save Preferences.
Testing
For testing we want the device edit page open for the new Virtual Device, a second browser tab or window with the Current Logs stream for the HE hub and thirdly a method for confirming the status of the air conditioner, whether that be the Kumo App / Web UI or some physical readout in the home such as a control panel on the wall or a remote.
On the device edit page click the Refresh button (not the one for your browser). Switch to the logs page and review the results. You will see a stream of text, then about a dozen or so entries, depending on the number of units you own. You will see logs for the unit serial number and label, operating mode, as well as various temperature settings and the fan mode. Compare these to what you expect to be the current state of the air conditioning unit(s). Note, some values may appear as "null", which I would expect at this point if the unit is turned off, I need to work on that still. The set temperature does not appear to be coming through either, again more work to be done there....
Switch back to the device edit page and confirm the authCode State Variable now appears and has a value assigned, this typically appears just below the refresh button.
Make a change to the air conditioner as you normally would, e.g. through the Kumo app or some other controlling device. Run the Refresh process again and review the results in the logs. You may need to run the refresh a few times for the changes to be detected, allowing for any delays in communication of changes with the Kumo servers.
Feedback and Next Steps
You are welcome to provide any feedback or test results, but it is probably safer via a PM rather than here on the thread. You don't need to include the long bit of text that is output, just the single line outputs that come after, like operating mode, etc.
I am thinking now I will leave this as being a good start for status info, with work still to be done, and move on to running commands such as changing to heating / cooling, changes in set temperature, etc.
Thanks,
Simon