feat(caddy): serve Audiobookshelf outside the guard chain

The Audiobookshelf phone app could never sign in over the public name. The guard
chain answered its /ping and /socket.io/ handshake with Anubis challenge HTML, so
the app evaluated 'isInit' in e.data on a non-object and reported "Failed to
contact server" while the container's request log recorded nothing at all. Anubis
demands a JavaScript proof-of-work and the authentik outpost works from a session
cookie: the chain is browser-only by construction, and a native client, a podcast
RSS reader or an OPDS client cannot pass it.

Audiobookshelf authenticates itself (local accounts plus authentik OIDC), so it
joins jelly/plex/*arr in the exempt set: the public site block dials the container
directly, keeping the X-Forwarded-Proto pin its OIDC origin check depends on, and
the @audiobooks route leaves the post-auth listener so one host has one owner. The
IdP rows that guarded the name go after this deploys, never before.

tests/e2e/specs/14-guard.spec.ts loses audiobooks as a guarded target and gains the
exemption assertion (app bytes to an anonymous client, the app's own 401, never
challenge HTML); tests/anubis.bats pins the route shape.

dankclaw/Caddyfile

@@ -22,13 +22,16 @@
 # CHALLENGE everyone else) → Caddy's internal listener http://:8016 (auth
 # decision; Host headers survive every hop) → authenticated traffic is
 # forwarded back to http://:8017 and routed straight to the app.
-# Apps with their own auth (Gitea, OpenWebUI, Jellyfin, *arr, Pi-hole) and the
-# Authentik IdP itself (auth.franksdank.cloud — its login flow must never sit
-# behind a challenge) are exempt by construction: their vhosts never route
-# through Anubis. ComfyUI left this exempt set on 2026-08-31 and Grafana left
-# it on 2026-09-01 (OAuth2 relying-party mode against authentik): both now sit
-# behind the guard chain; Grafana authenticates users itself via the OAuth2
-# code flow, so no identity header is forwarded to it.
+# Apps with their own auth (Gitea, OpenWebUI, Jellyfin, Plex, Audiobookshelf,
+# *arr, Pi-hole) and the Authentik IdP itself (auth.franksdank.cloud — its login
+# flow must never sit behind a challenge) are exempt by construction: their
+# vhosts never route through Anubis. The chain is browser-only by nature — a
+# native app client, a podcast RSS reader or a git client solves no JavaScript
+# proof, so anything that must serve one has to own its own authentication.
+# ComfyUI left this exempt set on 2026-08-31 and Grafana left it on 2026-09-01
+# (OAuth2 relying-party mode against authentik): both now sit behind the guard
+# chain; Grafana authenticates users itself via the OAuth2 code flow, so no
+# identity header is forwarded to it.
 # The pihole vhost keeps its basicauth edge; the hash placeholder below is
 # rendered by deploy.sh from CADDY_BASICAUTH_HASH (host .env, git-ignored) into
 # /home/dank/Containers/caddy/Caddyfile, which the container mounts.
@@ -264,17 +267,26 @@ files.franksdank.cloud {
 	}
 }
 
-# --- Audiobookshelf (guarded) ---
-# Anubis → Authentik → app, like romm/files. The container carries
-# ROUTER_BASE_PATH=/audiobookshelf, so this vhost serves the app under that
-# path; the bare root is redirected onto it in the post-auth listener, never
-# pre-auth. Guard state in the IdP: proxy provider `audiobooks-proxy`
-# (external_host https://audiobooks.franksdank.cloud/, internal_host
-# http://caddy:8017, application "Audiobookshelf Guard"), claimed by the
-# embedded outpost.
+# --- Audiobookshelf (exempt by construction: own auth) --------------------
+# Caddy → app: no Anubis, no outpost. The guard chain answers a native client's
+# /ping, /api/login and /socket.io/ handshake with challenge HTML, so behind it
+# the phone app parsed a non-object where the socket `init` payload belongs and
+# podcast RSS/OPDS feeds broke the same way. ABS authenticates itself (local
+# accounts plus authentik OIDC), so it joins jelly/plex/*arr outside the chain
+# (2026-11-03); the IdP rows that guarded this name — proxy provider
+# `audiobooks-proxy` and application "Audiobookshelf Guard" — are retired with
+# the change, after the route flips. Accepted exposure: /audiobookshelf/api/login
+# is internet-visible with no rate limiter on either side (this Caddy build has
+# no rate_limit module; ABS 2.37.2 ships no lockout) — the same class every other
+# own-auth vhost here lives with, so shared accounts need long unique passwords.
+# ROUTER_BASE_PATH=/audiobookshelf, so the bare root is a convenience hop onto it.
+# X-Forwarded-Proto must say https: ABS derives its OIDC origin from
+# x-forwarded-proto://Host and this hop is plain http, so without the pin its own
+# https callback is a 400 "Invalid callback URL - must be same-origin".
 audiobooks.franksdank.cloud {
-	reverse_proxy anubis:8923 {
-		header_up X-Real-Ip {remote_host}
+	redir / /audiobookshelf/ permanent
+	reverse_proxy 192.168.0.235:8000 {
+		header_up X-Forwarded-Proto https
 	}
 }
 
@@ -424,24 +436,6 @@ http://:8017 {
 		reverse_proxy 192.168.0.235:3923
 	}
 
-	@audiobooks host audiobooks.franksdank.cloud
-	handle @audiobooks {
-		# The app answers only under its ROUTER_BASE_PATH; the bare root is a
-		# convenience hop, taken post-auth so nothing reaches the app
-		# pre-authentication.
-		redir / /audiobookshelf/ permanent
-		# Audiobookshelf validates every OIDC callback against the origin it
-		# believes it is served from — getRequestOrigin() is
-		# x-forwarded-proto://Host — and a mismatch is a bodiless 400
-		# "Invalid callback URL - must be same-origin" before the IdP is ever
-		# contacted (measured 2026-11-03). This listener is fed over plain http
-		# by the outpost, so Caddy's own X-Forwarded-Proto here says http; the
-		# edge for this name is TLS-only, so https is the truthful value.
-		reverse_proxy 192.168.0.235:8000 {
-			header_up X-Forwarded-Proto https
-		}
-	}
-
 	@prowlarr host prowlarr.franksdank.cloud
 	handle @prowlarr {
 		reverse_proxy 192.168.0.112:9696

tests/anubis.bats

@@ -75,8 +75,10 @@ PY
 }
 
 @test "exempt vhosts never route through anubis (auth, plex, own-auth apps)" {
-    # The IdP login flow and git smart-HTTP clients cannot solve challenges;
-    # these vhosts bypass the chain by construction.
+    # The IdP login flow, git smart-HTTP clients, and any non-browser client (the
+    # Audiobookshelf phone app, podcast RSS readers) cannot solve a challenge, so
+    # services that enforce their own complete auth bypass the chain by
+    # construction — the gate would answer their API calls with HTML.
     local block
     block=$(awk '/^auth\.franksdank\.cloud/,/^}/' "$CADDY")
     echo "$block" | grep -q 'reverse_proxy authentik-server:9000'
@@ -84,4 +86,11 @@ PY
     block=$(awk '/^plex\.franksdank\.cloud/,/^}/' "$CADDY")
     echo "$block" | grep -q '192\.168\.0\.235:32400'
     ! echo "$block" | grep -q anubis
+    block=$(awk '/^audiobooks\.franksdank\.cloud/,/^}/' "$CADDY")
+    echo "$block" | grep -q '192\.168\.0\.235:8000'
+    ! echo "$block" | grep -q anubis
+    # The exemption is total: the post-auth listener must not still carry an
+    # audiobooks route. A leftover handle there is a second owner for one host,
+    # and its X-Forwarded-Proto pin would silently disagree with the edge.
+    ! grep -q '@audiobooks host audiobooks.franksdank.cloud' "$CADDY"
 }

tests/e2e/specs/14-guard.spec.ts

@@ -6,21 +6,21 @@ import { expect, test } from "@playwright/test";
 // navigation would skip. These tests drive the browser as an UNAUTHENTICATED
 // user (the guest project has no storage state) and navigate directly to each
 // guarded vhost's root path: the guard must present authentik's flow UI in
-// place and must never leak app content. plex is the documented exemption —
-// PMS enforces its own auth — so it must be reachable unauthenticated with
-// zero challenge pages, proving the exemption is deliberate, not accidental.
+// place and must never leak app content. plex and audiobooks are the documented
+// exemptions — PMS and Audiobookshelf enforce their own auth — so they must be
+// reachable unauthenticated with zero challenge pages, proving the exemption is
+// deliberate, not accidental.
 
 const BASE = "https://www.franksdank.cloud";
 
 // Every vhost that Caddy routes through anubis:8923 (see dankclaw/Caddyfile).
 // Keep this list in lockstep with the Caddyfile: a new guarded vhost must be
 // added here or the guard-chain audit is incomplete.
-const GUARDED = ["www", "search", "romm", "files", "seerr", "grafana", "prometheus", "loki", "notebook", "audiobooks"];
+const GUARDED = ["www", "search", "romm", "files", "seerr", "grafana", "prometheus", "loki", "notebook"];
 
 // Markers that prove app content leaked past the guard to an anonymous user. Each
-// marker must be a string the APP renders that the gate itself could never print —
-// for audiobooks that is the Audiobookshelf login's own SSO button label (the app's
-// door), which authentik's gate never renders because it IS the IdP.
+// marker must be a string the APP renders that the gate itself could never print:
+// authentik's gate never renders an app's UI text, because it IS the IdP.
 const LEAK_MARKERS: Record<string, string[]> = {
   "search.franksdank.cloud": ["SearXNG preferences"],
   "romm.franksdank.cloud": ["RomM"],
@@ -29,7 +29,6 @@ const LEAK_MARKERS: Record<string, string[]> = {
   "grafana.franksdank.cloud": ["Dashboards"],
   "prometheus.franksdank.cloud": ["Expression Browser", "Graph"],
   "notebook.franksdank.cloud": ["Open Notebook"],
-  "audiobooks.franksdank.cloud": ["Sign in with Authentik"],
 };
 
 test("homepage root (/) is guarded for unauthenticated users", async ({ page }) => {
@@ -102,3 +101,54 @@ test("plex is exempt from the guard chain and serves PMS content unauthenticated
   const resp = await page.request.get("https://plex.franksdank.cloud/");
   expect(resp.status(), "PMS must answer directly, not error").toBeLessThan(500);
 });
+
+// Audiobookshelf is exempt by construction (2026-11-03). The phone app is a
+// non-browser client and solves no JS proof-of-work, so behind the guard chain it
+// was answered with challenge HTML wherever the socket `init` payload belongs —
+// every remote sign-in died as a TypeError on a non-object, and the container's
+// request log never saw a byte of it. ABS enforces its own auth (local accounts
+// plus authentik OIDC), exactly like PMS above. Asserted from the CLIENT side: the
+// endpoints an app must call before it holds any credential are answered by the
+// app, and the app's own 401 — not a 200 of HTML — is what an anonymous API call gets.
+test("audiobookshelf answers an unauthenticated app client with app bytes, not gate bytes", async ({
+  request,
+}) => {
+  const ABS = "https://audiobooks.franksdank.cloud";
+
+  // The probe every Audiobookshelf client sends first. The app answers it at the
+  // ROOT whatever ROUTER_BASE_PATH says, so this is the vhost's own behaviour.
+  const ping = await request.get(`${ABS}/ping`, { timeout: 30_000 });
+  expect(ping.status(), "/ping must be answered by the app").toBe(200);
+  expect(await ping.json(), "/ping must carry the app's own payload").toEqual({ success: true });
+
+  // The socket.io handshake. Engine.IO answers this in a machine format; the gate
+  // answered it in HTML, which is the defect this exemption exists to kill.
+  const sock = await request.get(`${ABS}/audiobookshelf/socket.io/?EIO=4&transport=polling`, {
+    timeout: 30_000,
+  });
+  expect(
+    await sock.text(),
+    "the socket handshake was answered by the gate, not Engine.IO",
+  ).not.toContain("Making sure you're not a bot");
+  expect(
+    sock.headers()["content-type"] ?? "",
+    "the socket handshake must not arrive as HTML",
+  ).not.toMatch(/text\/html/);
+
+  // An API call with no credential: the app refuses it. A gate would answer 200
+  // with HTML, so the status code alone distinguishes the two owners.
+  const api = await request.get(`${ABS}/audiobookshelf/api/libraries`, { timeout: 30_000 });
+  expect(api.status(), "the app's own auth gate must own unauthenticated API calls").toBe(401);
+});
+
+test("audiobookshelf login renders the app's own sign-in to an anonymous browser", async ({ page }) => {
+  test.setTimeout(120_000);
+  await page.goto("https://audiobooks.franksdank.cloud/audiobookshelf/login");
+  expect(new URL(page.url()).hostname).toBe("audiobooks.franksdank.cloud");
+
+  const body = await page.locator("body").innerText();
+  expect(body, "the bot challenge still fronts this vhost").not.toContain("Making sure you're not a bot");
+  expect(await page.locator('input[name="uidField"]').count(), "the IdP gate form must not front the app").toBe(0);
+  // The app answers, and its login screen carries SSO beside the local form.
+  await expect(page.getByText("Sign in with Authentik")).toBeVisible({ timeout: 90_000 });
+});