Google Play Games Services API

In Google Cloud Console Credentials, create an OAuth 2.0 client ID for your app/server, then configure the Play Games Services integration for your game as described in the Google Play Game Services Web REST API docs. Request one of the scopes shown by the API methods, such as https://www.googleapis.com/auth/games or https://www.googleapis.com/auth/games_lite, to mint access tokens for calls to the Games API.

In Google Cloud Console Credentials, create an API key for your Google Cloud project. The Games discovery document says the key query parameter is accepted and is required unless you provide an OAuth 2.0 token. Restrict the key appropriately in Google Cloud Console before using it with the Games API.