How does Spring Security's oauth2Login() simplify implementing 'Login with Google'?

oauth2Login() implements the entire Authorization Code + OIDC flow internally — redirecting to the provider's authorization endpoint (via the conventional /oauth2/authorization/{registrationId} URL), handling the callback, exchanging the code for tokens, validating the ID token, and populating an authenticated OAuth2AuthenticationToken/OidcUser principal — all from a few configuration properties (client-id, client-secret, scopes) rather than implementing any of the OAuth2 protocol steps by hand.