Sign in with Yahoo
Preview. League membership cannot be checked until Yahoo
grants API access, so this deployment accepts a preview key instead:
/auth/preview?key=…. It shows demonstration data and is marked
on every page.
Your Yahoo account stays yours. We ask Yahoo once whether
your account is a manager in this league. Then we delete the sign-in details
Yahoo gave us. The only thing we keep is a cookie that says you are signed
in. League data is read with the commissioner's own Yahoo access, never
yours.