Signing in showed the "Welcome back!" toast but never left /login. The
session cookie was host-only on the API subdomain, so the Next middleware
guard on the site origin saw no cookie and bounced /dashboard straight
back to /login?redirect=/dashboard.
- Add AUTH_COOKIE_DOMAIN, wiring Better Auth's crossSubDomainCookies so
the cookie also reaches the site origin. Unset in dev, where localhost
is single-host and must stay host-only.
- Navigate after authentication with a full page load, via a shared
authRedirect helper: only a top-level request carries the httpOnly
cookie. Used by the login, register, magic-link and Google flows.
- Show "Redirecting..." on the login and register pages and keep the
submit button disabled until the browser replaces the page, instead of
re-enabling it mid-navigation.
- Guard against a redirect loop with a sessionStorage marker. A React ref
cannot do this: the full page load resets component state. If the
destination bounces back, explain it rather than navigating again.
- Middleware: accept any *.session_token cookie so a cookiePrefix change
cannot lock everyone out, and preserve the destination's query string.
- Trust any loopback port in dev, so reaching the dev server through a
forwarded port does not fail Better Auth's CSRF origin check.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
