The app actually does not have any user-management as such. So to login we've put the auth proxy in front of it. You should be able to login with your regular cloudron user, if he is granted access to the app. Otherwise do you see any errors in the webinspector?
@rmdes since this is actually mostly unrelated to the app as such, can you login to other apps using the auth proxy like if you would install simple torrent test-wise?
And to doublecheck as well, do you have 2fa set in Cloudron?