A year and a half later and I've actually cracked this nut... you can "update" the app by replacing the Splunk SDK located here:
Once this has been updated the app should start working with the latest versions of Splunk. Make sure you restart Splunk.
Hello @dgwhjj, I was curious how you managed to get this to work... I understand, I think, the directory you're talking about... in my case, with Windows, it's this folder within the app itself:
However I'm not entirely understanding your fix... are you installing a new/separate Node JS to this folder location? This almost makes sense to me because there is a node_modules folder there (it's the only other folder there actually) but I wouldn't think that updating this would make the necessary updates to server.js (which the app needs to run). The Node JS in Splunk is already updated, so I'm assuming you are some how updating Node JS within the Auth0 app?