React bindings for gapi.auth2 (Google's OAuth 2.0 JavaScript client)

You want to use the gapi.auth2 api to implement "Sign in with Google" in your React app. However, you don't want to use the api directly because,

• You don't want to load <script /> tags manually, as suggested in the documentation
• You prefer to write declarative code and gapi.auth2 is an imperative api

// TODO