Add internal/cfsetup, the verifiable core of an optional one-click
Cloudflare Tunnel + Access provisioning flow for the SysAdmin edge
(spec §14). It is domain-agnostic (every FQDN is composed from the
configured root_domain) and IdP-agnostic (any valid Access JWT aud is
accepted, whichever IdP fronts it), so a SysAdmin who brings their own
domain or Zero-Trust scheme stays fully supported.
The load-bearing safety property is a fail-closed guard on the
recommended Access policy. validateFailClosed is an allowlist that
refuses any policy that could be public: a bypass/non-allow decision, an
empty include, an "everyone" include not narrowed by a constraining
require (include rules are OR, so "everyone" beside an identity is still
public), or any include rule it cannot positively recognize as a scoped
identity. Setup runs the guard before any side effect, so a public
policy aborts the run with nothing created.
The tunnel ingress routes only the web hostnames to the local panel
origin and terminates in the mandatory fail-shut 404 catch-all; the raw
game host is never proxied. Gating preconditions (cloudflared present,
tunnel login completed, API token) are hard checks with no side effects
on failure.
The actual cloudflared exec, DNS routing, and Access API calls live in
runner.go and are integration-only: they require the operator's own live
Cloudflare account and interactive browser consent, which cannot be
unit-tested. The policy guard, ingress generation, request bodies, and
gating are unit-tested.
