I have two different laravel 6 websites "A"(database use PostgresSQL) and "B"(database use MySQL), I want to make user sign in at "A" website then user will be automatically logged in "B" websites, ex: google account.
You'd basically want to create an app that handles auth... that would be your SSO and then mess with the Laravel auth code of your other apps to integrate the SSO you created. SSO is something most companies have to create on their own.
It would be much easier just to use Socialite on both apps and roll with that.