Google Authentication in ASP.NET Core with React

'Sign in with Google' looks like one button but hides a real handshake between your React frontend, Google, and your ASP.NET Core API. In this video I wire up Google authentication end to end on .NET 9: React gets an ID token from Google, sends it to the API, and the API verifies that token is genuinely from Google before ever trusting it or issuing its own session. I cover why you never trust a Google ID sent straight from the client without server-side verification, and how the backend maps a verified Google account to your own user record. If you've been putting off social login because the flow feels murky, this lays out exactly what talks to what.