Since you mention that you have the authorize-project plugin installed, chances are that you are using some other plugins that might break things?
I would suggest to verify that it fails for you on a clean install. If not, then start adding plugins until you find out which one that might interfere.
I still can't reproduce your results, and I'm doing it in a clean install with only this plugin installed and all its dependencies. Also note that we are running this in production with god knows which other plugins (though not the authorize-project), and we don't see any issue using credentials.