To enable Google sign-in, create OAuth client credentials at Google Cloud Console and set these in your .env:

GOOGLE_CLIENT_ID=…
GOOGLE_CLIENT_SECRET=…
GOOGLE_REDIRECT_URI=http://localhost:5000/auth/google/callback
APP_SECRET=<random 32+ char string>

Add http://localhost:5000/auth/google/callback as an authorized redirect URI in the Google Cloud project, then restart py app.py.