Behind Jambotron's Caddy the app saw http while the browser used https,
so same-domain requests looked cross-origin and @CrossOrigin answered
403 on /api/auth/signin. server.forward-headers-strategy=framework makes
the app use X-Forwarded-Proto/Host; app.origin can be set via APP_ORIGIN.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>