Usability in testing scenarios - unhandled promise rejections

Hey @nicolasgarnier !

I've been using your component for a hot minute, implementing OAuth in an app I'm contributing to.

There are 2 unhandled promise rejections in this plugin that will automatically fail in a test environment where .env variables are missing.

Is there a special way this plugin should be tested?
If not would it be feasible to implement a catch for each of the 2 used promises in order for it not to have to be mocked out completely?

I tested it in a fork locally and it works like a charm for me, if I should open a PR for this, please let me know!