Google APIs use the OAuth 2.0 protocol for authentication and authorization. Google supports common OAuth 2.0 scenarios such as those for web server, installed, and client-side applications.
To begin, obtain OAuth 2.0 client credentials from the Google API Console. Then your client application requests an access token from the Google Authorization Server, extracts a token from the response, and sends the token to the Google API that you want to access. For an interactive demonstration of using OAuth 2.0 with Google (including the option to use your own client credentials), experiment with the OAuth 2.0 Playground.
This page gives an overview of the OAuth 2.0 authorization scenarios that Google supports, and provides links to more detailed content. For details about using OAuth 2.0 for authentication, see OpenID Connect.
