For google sign in, as google deprecated the platform.js library so we are going to use the google identity service library, and get the access_token using the Token Model.

const client = google.accounts.oauth2.initTokenClient({
  client_id: 'YOUR_GOOGLE_CLIENT_ID',
  scope: 'https://www.googleapis.com/auth/calendar.readonly',
  callback: (response) => {
    ...
  },
});

To trigger the UX flow, the client.requestAccessToken(); is called on each click of the Google signin button.

One thing I didn't understand is how to handle the access_token expiry -

As per the doc -

By design, access tokens have a short lifetime. If the access token expires prior to the end of the user's session, obtain a new token by calling requestAccessToken() from a user-driven event such as a button press.

Q.1 Does the above mean we need to call this function explicitly from the callback function? Or how would we know the access_token is expired?

Also with platform.js, we had an option to check if the user is already logged in google -

GoogleAuth = gapi.auth2.getAuthInstance();
currentUser = GoogleAuth.currentUser.get();

if (currentUser && currentUser.isSignedIn()) {
   // user is already loggedin in google
} else {
   googleAuthPromise = GoogleAuth.signIn();
   googleAuthPromise.then(function (user) {
     // now user is loggedin in google
   });
}

Q.2 But with the new library, these methods are not available, how can we achieve that if a user is already logged in to google (by not involving any custom session or cookie variables)?