Can I use Google authentication in apps not using Lovable Cloud?

Yes, Google authentication works with Supabase integration (which isn't the same as Lovable Cloud). Both use Supabase's authentication system. Enable the Google provider in your Supabase project's Authentication → Providers, add your OAuth credentials, and configure redirect URIs. Lovable can then auto-scaffold the 'Sign in with Google' button when you ask in chat.