pages.signIn is meant to point at a CUSTOM sign-in page. Setting it to
'/api/auth/signin' — Auth.js's own built-in endpoint — makes Auth.js
redirect there whenever it wants the sign-in page, which is the same
endpoint, producing ERR_TOO_MANY_REDIRECTS in browsers.
Omitting the setting falls back to Auth.js's default sign-in handler,
which renders the provider-picker HTML at /api/auth/signin instead of
redirecting.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>