I’d recommend you have a look at the cluster side logs. There should be some more information there on what happened with the authentication.
Also, one thing you might use to diagnose this is our experimental tool which has the working name at the moment SDK doctor. Maybe try running it in that env with the username/password you expect to work?
You’ll find pre-built binaries on the release page.
Usually the summary at the end is pretty easy to interpret. If you need help with interpretation, please feel free to post it or a link to it here.