Use the Supabase Auth user for this project (same NEXT_PUBLIC_SUPABASE_* as in .env.local). Password sign-in only works if that user has a password.
NEXT_PUBLIC_SUPABASE_*
.env.local
No password? Use a one-time email link. In Supabase → Authentication → URL configuration, allow redirect /auth/callback for this site origin.
/auth/callback