How to Implement Google SSO in shiny proxy application

Question

I have a shiny proxy application that runs on a domain let's say A.com and then I have an express application that runs on B.com.

I created Google OAuth2.0 client credentials for the app and added the following in application.yml:

proxy:
...
...
  authentication: openid
  openid:
    auth-url: https://accounts.google.com/o/oauth2/v2/auth
    token-url: https://www.googleapis.com/oauth2/v4/token
    jwks-url: https://www.googleapis.com/oauth2/v3/certs
    client-id: <CLIENT_ID>
    client-secret: <CLIENT_SECRET>
...
...

I can successfully log in with google into my shiny-proxy application with this

and

I have also set up the express application with passport-google-oidc and successfully log in to it with google.

Now I am extremely puzzled about how can I implement SSO between them. How is this possible with Shiny proxy and expressJS? Is it possible?