The hope of a seamless login portal is completely and utterly dead.

There's a reason that Auth0 and Okta haven't been able to figure it out, and it's not just laziness - it's because browser vendors keep changing critical components in majorly breaking ways.

Until portals arrive (if ever), there is 0 hope for a seamless login.

With that said, there's little point in even suggesting that someone use the google-specific pop-up modal for Google Sign-In.

Better to do the redirects server-side.