General scheme
A sign-in starts in your app: it sends the browser to the sign-in page with a standard OpenID Connect redirect. The user confirms in a channel, and the browser returns to your app with a code that your app exchanges for tokens.

Signing in on a computer

The user scans the QR code with their phone camera, picks a Google account and taps Yes on the confirmation page.
Signing in on a phone

The user taps "Sign in with Google", picks an account and taps Yes on the confirmation page. Google asks for consent only on the first sign-in.
Claims your app can get
