First, under the Google developer console, you'll want to create a new project (if you don't already have one). This is what allows you to associate an OAuth flow with your Phoenix application. You can name it whatever you like, but again, you should try to keep your development (or otherwise non-production) environments named in such a way that you can pick them out easily enough:
The next step after you've created your project is to navigate to the application's Credentials screen. Here, you'll click on Create Credentials (if you don't already have credentials set up and ready to go). You will be presented ...