How do I create a Public API key on the Google Developer Console?

[jshou via StackOverflow]

I'm trying to set up Google+ Authentication by following these instructions: https://developers.google.com/+/api/oauth

I've activated the Google+ API within my project on the Google Developers Console, but when I click Credentials in the side bar, the "Create new Key" button is grayed out. Am I missing a step somewhere?

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