Now that we’ve learned to create a Phoenix app, add a Users model, and deploy it all to Heroku, it’s time to add authentication. In this example we’ll learn how to hook our Phoenix app up to Fitbit with OAuth2. Specifically, we’re going to use @scrogson’s OAuth2 Library for Elixir and the Authorization Code Grant flow as described in Fitbit’s OAuth2 documentation. To get started, follow steps 1-4