Debug PKCE, tokens, and nested xchk portfolio claims (payload.xchk.portfolio). For apps that already verify users on xChk — not a generic Google-login replacement. Register apps at login-with-xchk.html.
Add this exact redirect URI to your OAuth client. Use this playground URL for debugging without deploying a callback.
Guide: login-with-xchk.md · LLM instructions · Example: crabbyed.com