Re: Automatic Sign-in? How else can Google get us:
at the heart of it all is 'OAuth' and subscribing to Google or Microsoft's services, such that if you're already logged in via google, or 'Microsoft Login' then oauth can silently track you without your knowledge. This article talks about doing this with 'Bing Ads':
https://docs.microsoft.com/en-us/bingads/guides/authentication-oauth?view=bingads-12
It may be 'bending the rules' a bit (to heavily track you without ANY consent) but I doubt they'd get CAUGHT doing it if they did...