Offering only Google leaves out the majority of small business (and big business!) coders worldwide who rely on Microsoft's small business ecosystem.

To solve in a generalized way consider OpenID Connect (OIDC) that lets you put a stack of "Sign in with [account]" or "Continue with [account]" buttons, easily.

You end up with this:

https://www.xsplit.com/user/auth

And you don't need the complicated "SSO" stuff.

Another example:

https://id.atlassian.com/login

But it's better to not need to implement username/password login at all, meaning you don't have any usernames or passwords to steal or lose.

That flow sends an auth token by email. I've implemented other versions that use SMS for login with numbers after that flow takes place.