feat(audiobookshelf): provision authentik SSO and send the redirect subfolder

The live round trip died on authentik with Redirect URI Error. ABS builds redirect_uri as <origin><authOpenIDSubfolderForRedirectURLs>/auth/openid/callback, and that key is unset on a database created before SSO (the 2.17.4 migration only fills a DB that already had OIDC enabled), so the URL carried the literal string undefined. Arming through the API therefore has to send the value; it is the mounted base path, so it is derived from ABS_URL rather than becoming a second knob an operator has to keep in sync.

authentik-audiobookshelf-sso.sh is the IdP half kept in git: provider, groups, the abs_groups scope mapping and the redirect URIs. That state lives in authentik's database, and a blueprint re-import reverts hand-made rows silently, so it needs a re-runnable door. Tokens are HS256 because no provider on the fleet carries a signing key, which makes the client secret the signature key.

The stub server now records the auth-settings PATCH body, so the seam asserts the subfolder that reaches the wire follows ABS_URL for both the prefixed and root shapes, and a second seam pins that the provider script and the bootstrapper build the same redirect path.

scripts/audiobookshelf-init.sh

@@ -21,26 +21,64 @@
 # The credential is generated once into a mode-600 host file and never enters
 # the repo, the URL, or a process argument list. Same pattern as calibre-server.
 #
+# Single sign-on (authentik) is armed by the same run, and only when the credential
+# file carries ABS_OIDC_CLIENT_SECRET, so a local-only deployment is unchanged by a
+# re-run. These OIDC facts came from the same pinned image, and each one is a trap:
+#   * isOpenIDAuthSettingsValid demands issuer + authorization + token + userinfo +
+#     jwks + clientID + clientSecret + signingAlgorithm at once. Miss one and the
+#     server SILENTLY strips 'openid' from authActiveAuthMethods and falls back to
+#     ['local'] while answering 200 everywhere — so the only honest check is what
+#     /status says AFTER the write, which is what this script does.
+#   * the algorithm is HS256, not the image's RS256 default: no provider on the
+#     fleet's authentik carries a signing key, so the client secret IS the signature
+#     key (scripts/authentik-audiobookshelf-sso.sh). Left at RS256, every id_token
+#     fails verification and the failure looks like a broken IdP.
+#   * the auth block lives on PATCH /api/auth-settings. PATCH /api/settings has a
+#     20-key allowlist (PATCHABLE_SETTINGS_KEYS) with NO auth key in it, so writing
+#     the OIDC config there answers 200 and changes nothing — measured on this host
+#     2026-11-02. The keys /api/auth-settings accepts are exactly its own
+#     authenticationSettings getters; anything else is skipped with a debug line.
+#   * authOpenIDSubfolderForRedirectURLs must be sent explicitly. The 2.17.4 migration only
+#     fills it on a DB that ALREADY had OIDC on, so a database created before SSO leaves it
+#     UNDEFINED and the server builds redirect_uri
+#     "http://host/undefined/auth/openid/callback" — authentik answers the authorize request
+#     with "Redirect URI Error" (measured 2026-11-02). This script derives the value from
+#     ABS_URL's path, so it cannot drift from the unit's ROUTER_BASE_PATH.
+#   * 'local' stays in authActiveAuthMethods on purpose: if authentik is ever down,
+#     the root account must still be able to sign into its own server.
+#
 # usage: audiobookshelf-init.sh          # create what is missing, then scan
 #        ABS_SCAN=0 audiobookshelf-init.sh   # bootstrap without a scan
+#        ABS_OIDC=0 audiobookshelf-init.sh   # never touch the auth methods
 #
 # environment (defaults are the deployed shape):
-#   ABS_URL      server base URL              (http://127.0.0.1:8000)
+#   ABS_URL      server base URL INCLUDING the mounted base path
+#                (http://127.0.0.1:8000/audiobookshelf)
 #   ABS_SECRET   credential file              (/home/dank/.config/secrets/audiobookshelf)
 #   ABS_LIBRARY  library name to ensure        (Audiobooks)
 #   ABS_FOLDER   folder to bind inside the server (/audiobooks)
 #   ABS_SCAN     1 triggers a scan (default), 0 skips it
+#   ABS_OIDC     auto (default) arms SSO when the credential file has a client
+#                secret, 1 requires one, 0 leaves the auth methods alone
+#   ABS_OIDC_ISSUER   authentik issuer URL for this client
+#   ABS_OIDC_CLIENT_ID provider client id (audiobookshelf)
+#   ABS_OIDC_ALG       id_token signing algorithm the IdP actually uses (HS256)
+#   ABS_OIDC_SUBFOLDER override for the redirect-URI subfolder (default: ABS_URL's path)
 #
 # exit 0  every step is satisfied (created or already present)
 # exit 1  a step was refused or the server misbehaved (named on stderr)
 # exit 2  usage / unreadable credential file
 set -euo pipefail
 
-ABS_URL=${ABS_URL:-http://127.0.0.1:8000}
+ABS_URL=${ABS_URL:-http://127.0.0.1:8000/audiobookshelf}
 ABS_SECRET=${ABS_SECRET:-/home/dank/.config/secrets/audiobookshelf}
 ABS_LIBRARY=${ABS_LIBRARY:-Audiobooks}
 ABS_FOLDER=${ABS_FOLDER:-/audiobooks}
 ABS_SCAN=${ABS_SCAN:-1}
+ABS_OIDC=${ABS_OIDC:-auto}
+ABS_OIDC_ISSUER=${ABS_OIDC_ISSUER:-https://auth.franksdank.cloud/application/o/audiobookshelf/}
+ABS_OIDC_CLIENT_ID=${ABS_OIDC_CLIENT_ID:-audiobookshelf}
+ABS_OIDC_ALG=${ABS_OIDC_ALG:-HS256}
 
 die() { printf 'refused: %s\n' "$*" >&2; exit 1; }
 
@@ -49,6 +87,11 @@ case "$ABS_SCAN" in
     *) printf 'refused: ABS_SCAN wants 0 or 1, got %s\n' "$ABS_SCAN" >&2; exit 2 ;;
 esac
 
+case "$ABS_OIDC" in
+    auto | 0 | 1) ;;
+    *) printf 'refused: ABS_OIDC wants auto, 0 or 1, got %s\n' "$ABS_OIDC" >&2; exit 2 ;;
+esac
+
 # ---- credential -------------------------------------------------------------
 umask 077
 if [ ! -f "$ABS_SECRET" ]; then
@@ -72,8 +115,10 @@ chmod 600 "$ABS_SECRET"
 # python3 rather than curl so the password and the bearer token never appear in
 # any argv (they would be world-readable in /proc/<pid>/cmdline otherwise).
 ABS_URL="$ABS_URL" ABS_SECRET="$ABS_SECRET" ABS_LIBRARY="$ABS_LIBRARY" \
-ABS_FOLDER="$ABS_FOLDER" ABS_SCAN="$ABS_SCAN" python3 - <<'PY'
+ABS_FOLDER="$ABS_FOLDER" ABS_SCAN="$ABS_SCAN" ABS_OIDC="$ABS_OIDC" \
-import json, os, sys, urllib.error, urllib.request
+ABS_OIDC_ISSUER="$ABS_OIDC_ISSUER" ABS_OIDC_CLIENT_ID="$ABS_OIDC_CLIENT_ID" \
+ABS_OIDC_ALG="$ABS_OIDC_ALG" python3 - <<'PY'
+import json, os, sys, urllib.error, urllib.parse, urllib.request
 
 BASE = os.environ["ABS_URL"].rstrip("/")
 LIB = os.environ["ABS_LIBRARY"]
@@ -184,5 +229,81 @@ code, items = call("GET", "/api/libraries/%s/items?limit=1" % lib["id"], token=t
 if code == 200 and isinstance(items, dict):
     print("items: %s (a fresh scan raises this from 0; watch it, not /healthcheck)"
           % items.get("total"))
+
+# ---- single sign-on (authentik) --------------------------------------------------
+# The provider this points at is provisioned by scripts/authentik-audiobookshelf-sso.sh;
+# the two share exactly one value, the client secret in the credential file.
+mode = os.environ["ABS_OIDC"]
+oidc_secret = cred.get("ABS_OIDC_CLIENT_SECRET") or ""
+if mode == "0":
+    print("oidc: skipped (ABS_OIDC=0)")
+elif not oidc_secret:
+    if mode == "1":
+        sys.exit("refused: ABS_OIDC=1 but %s has no ABS_OIDC_CLIENT_SECRET — run "
+                 "scripts/authentik-audiobookshelf-sso.sh first" % os.environ["ABS_SECRET"])
+    print("oidc: not configured (no ABS_OIDC_CLIENT_SECRET in the credential file)"
+          " — local auth only")
+else:
+    client_id = os.environ["ABS_OIDC_CLIENT_ID"]
+    issuer = os.environ["ABS_OIDC_ISSUER"].rstrip("/") + "/"
+    # redirect_uri = <origin><subfolder>/auth/openid/callback, and the subfolder IS the
+    # base path the app is mounted under — taken from ABS_URL so unit and config agree.
+    subfolder = os.environ.get("ABS_OIDC_SUBFOLDER")
+    if subfolder is None:
+        subfolder = urllib.parse.urlparse(os.environ["ABS_URL"]).path.rstrip("/")
+    origin = issuer.split("/application/")[0]
+    body = {
+        "authActiveAuthMethods": ["local", "openid"],
+        "authOpenIDIssuerURL": issuer,
+        "authOpenIDAuthorizationURL": origin + "/application/o/authorize/",
+        "authOpenIDTokenURL": origin + "/application/o/token/",
+        "authOpenIDUserInfoURL": origin + "/application/o/userinfo/",
+        "authOpenIDJwksURL": issuer + "jwks/",
+        "authOpenIDLogoutURL": issuer + "end-session/",
+        "authOpenIDClientID": client_id,
+        "authOpenIDClientSecret": oidc_secret,
+        "authOpenIDTokenSigningAlgorithm": os.environ["ABS_OIDC_ALG"],
+        "authOpenIDSubfolderForRedirectURLs": subfolder,
+        "authOpenIDButtonText": "Sign in with Authentik",
+        # not auto-launch: the login page keeps offering the local form, which is the
+        # break-glass path when the IdP is unreachable.
+        "authOpenIDAutoLaunch": False,
+        # a household user's first SSO sign-in creates their account; the group claim
+        # decides the role, and a user in neither group is denied (fail closed).
+        "authOpenIDAutoRegister": True,
+        "authOpenIDGroupClaim": "abs_groups",
+        # The app's own scheme lives HERE, never in the IdP: ABS swaps it for
+        # <base>/auth/openid/mobile-redirect before the provider sees a redirect_uri.
+        "authOpenIDMobileRedirectURIs": ["audiobookshelf://oauth"],
+    }
+    code, res = call("PATCH", "/api/auth-settings", body, token=token)
+    if code != 200:
+        sys.exit("refused: PATCH /api/auth-settings answered %s (%s)" % (code, res))
+    # Verify twice: what was stored, and what the server will honour. A config that
+    # misses any of the eight required OIDC values is accepted with 200 and then
+    # silently dropped at the next load, leaving authMethods=['local'].
+    code, stored = call("GET", "/api/auth-settings", token=token)
+    if code != 200 or not isinstance(stored, dict):
+        sys.exit("refused: GET /api/auth-settings answered %s (%s)" % (code, stored))
+    for key, want in (("authOpenIDIssuerURL", issuer),
+                      ("authOpenIDTokenSigningAlgorithm", os.environ["ABS_OIDC_ALG"]),
+                      ("authOpenIDSubfolderForRedirectURLs", subfolder),
+                      ("authOpenIDButtonText", "Sign in with Authentik")):
+        if stored.get(key) != want:
+            sys.exit("refused: stored %s=%r, expected %r" % (key, stored.get(key), want))
+    if sorted(stored.get("authActiveAuthMethods") or []) != ["local", "openid"]:
+        sys.exit("refused: stored authActiveAuthMethods=%r, expected local+openid "
+                 "('openid' is dropped when the block is incomplete)"
+                 % stored.get("authActiveAuthMethods"))
+    code, after = call("GET", "/status")
+    methods = after.get("authMethods") if isinstance(after, dict) else None
+    if not isinstance(methods, list) or "openid" not in methods:
+        sys.exit("refused: /status reports authMethods=%s after a stored config that "
+                 "looks complete — restart the service, the strategy is only armed at "
+                 "load for a config that was invalid when the server read it" % methods)
+    print("oidc: armed (issuer %s | alg %s | claim abs_groups | redirect subfolder %r | "
+          "client %s | secret %s chars | authMethods %s)"
+          % (issuer, os.environ["ABS_OIDC_ALG"], subfolder, client_id, len(oidc_secret),
+             methods))
 PY
 exit 0

scripts/authentik-audiobookshelf-sso.sh

@@ -0,0 +1,203 @@
+#!/usr/bin/env bash
+# authentik-audiobookshelf-sso.sh — provision the authentik side of Audiobookshelf SSO.
+#
+# Why a script: this state lives in authentik's DATABASE, not in any repo file, and a
+# blueprint re-import or a rebuild-from-scratch reverts hand-made provider rows
+# silently. Same reasoning (and same door) as
+# authentik-set-login-session-duration.sh: ssh into Dankclaw, `ak shell` from stdin.
+# Re-run this after such a rebuild.
+#
+# The contract with Audiobookshelf, read off the pinned image (2.37.2,
+# dist-server/server/auth/OidcAuthStrategy.js + objects/settings/ServerSettings.js)
+# rather than a forum, because each of these is a dead-login trap:
+#
+#   * TWO redirect URIs on the provider: <base>/auth/openid/callback (browser) and
+#     <base>/auth/openid/mobile-redirect (mobile). ABS SWAPS the app's own
+#     audiobookshelf://oauth for the mobile-redirect URL before the IdP ever sees a
+#     redirect_uri, so registering the app scheme with authentik — the obvious move —
+#     is what makes phone logins fail. The app scheme belongs in ABS's
+#     authOpenIDMobileRedirectURIs list (its built-in default), not here.
+#   * <base> CARRIES THE BASE PATH. ABS builds redirect_uri as
+#     <origin><authOpenIDSubfolderForRedirectURLs>/auth/openid/callback, and that subfolder is
+#     the ROUTER_BASE_PATH the container is mounted at — /audiobookshelf, which is also the only
+#     base path the shipped SPA can boot under. Left unset (the fresh-DB default) the URL
+#     becomes "/undefined/…"; a provider registered without the prefix mismatches the same way
+#     (measured 2026-11-02, "Redirect URI Error"). audiobookshelf-init.sh derives its copy from
+#     ABS_URL, so the two sides each move with one variable.
+#   * ABS requests the scopes "openid profile email <GroupClaim> [<PermsClaim>]": the
+#     CLAIM NAME is a scope name. So authentik needs a scope mapping whose scope_name
+#     is exactly the claim name, or the claim never arrives and the callback dies on
+#     "Group claim <name> not found in userinfo".
+#   * the claim's VALUES must be ABS role names — the callback picks the first of
+#     ['admin','user','guest'] present in the list. Group names like
+#     audiobookshelf_admins are therefore translated by the mapping, never passed
+#     through. A user in neither group gets [] and is denied (fail closed).
+#   * tokens are HS256 here: no provider on this box carries a signing_key (census
+#     2026-11-02), which makes the client secret the signature key. ABS's own default
+#     is RS256, so the ABS side MUST be set to HS256 or every id_token fails
+#     verification.
+#   * provider.authorization_flow must be non-NULL or /application/o/authorize/
+#     answers a 500 with 'NoneType' object has no attribute 'slug' (measured on
+#     grafana, same authentik build).
+#
+# Idempotent: every object is created or asserted. Safe to re-run.
+#
+# usage: ABS_OIDC_CLIENT_SECRET=<secret> authentik-audiobookshelf-sso.sh
+#        (the secret is the value stored in
+#         /home/dank/.config/secrets/audiobookshelf on Dankserver — get it with
+#         ssh dankserver awk -F= '/^ABS_OIDC_CLIENT_SECRET=/{print $2}' \
+#             ~/.config/secrets/audiobookshelf)
+#
+# environment:
+#   ABS_OIDC_CLIENT_SECRET  REQUIRED. The provider's client secret.
+#   ABS_OIDC_CLIENT_ID      provider/client id           (audiobookshelf)
+#   ABS_OIDC_GROUPS_CLAIM   claim ABS reads for roles    (abs_groups)
+#   ABS_OIDC_USERNAME       authentik user made admin    (akadmin)
+#   ABS_OIDC_USERS          space-separated authentik usernames given the USER group
+#                           (default: nobody — an empty list is fail-closed, and the
+#                            household decides who listens to audiobooks)
+#   ABS_BASE                ABS URL as the browser sees it, base path included
+#                           (http://192.168.0.235:8000/audiobookshelf — LAN-only by policy:
+#                            no vhost, no reverse proxy in front)
+#   AUTHENTIK_HOST          ssh target                    (dankclaw)
+set -euo pipefail
+
+SECRET="${ABS_OIDC_CLIENT_SECRET:?set ABS_OIDC_CLIENT_SECRET (see the header)}"
+[ "${#SECRET}" -ge 32 ] || { echo "refused: ABS_OIDC_CLIENT_SECRET is too short to be a secret" >&2; exit 2; }
+
+CLIENT_ID="${ABS_OIDC_CLIENT_ID:-audiobookshelf}"
+CLAIM="${ABS_OIDC_GROUPS_CLAIM:-abs_groups}"
+ADMIN_GROUP="audiobookshelf_admins"
+USER_GROUP="audiobookshelf_users"
+SSO_USER="${ABS_OIDC_USERNAME:-akadmin}"
+MEMBERS="${ABS_OIDC_USERS:-}"
+BASE="${ABS_BASE:-http://192.168.0.235:8000/audiobookshelf}"
+HOST="${AUTHENTIK_HOST:-dankclaw}"
+
+# The claim expression: translate group membership into ABS role names. It is stored
+# verbatim so a later read of the provider shows exactly this policy.
+read -r -d '' EXPR <<PYEXPR || true
+groups = {g.name for g in user.groups.all()}
+roles = []
+if "$ADMIN_GROUP" in groups:
+    roles.append("admin")
+if groups & {"$ADMIN_GROUP", "$USER_GROUP"}:
+    roles.append("user")
+return {"$CLAIM": roles}
+PYEXPR
+
+ssh "$HOST" 'podman exec -i authentik-server ak shell' <<PYEOF
+from authentik.core.models import Application, Group, User
+from authentik.flows.models import Flow
+from authentik.providers.oauth2.models import (
+    ClientType, OAuth2Provider, RedirectURI, RedirectURIMatchingMode, RedirectURIType, ScopeMapping)
+
+ADMIN_GROUP, USER_GROUP = "$ADMIN_GROUP", "$USER_GROUP"
+CLAIM, CLIENT_ID, SECRET, BASE = "$CLAIM", "$CLIENT_ID", "$SECRET", "$BASE"
+SSO_USER = "$SSO_USER"
+MEMBERS = """$MEMBERS""".split()
+EXPR = '''$EXPR'''
+# The expression reads user.groups, NOT user.ak_groups: authentik 2026.8 logs
+# "User.ak_groups is deprecated … use User.groups" on every evaluation of the old
+# name (measured on this run), and a stored mapping that leans on a deprecated
+# accessor is a future upgrade failure sitting inside the login path.
+
+for name in (ADMIN_GROUP, USER_GROUP):
+    Group.objects.get_or_create(name=name)
+admin_g, user_g = Group.objects.get(name=ADMIN_GROUP), Group.objects.get(name=USER_GROUP)
+
+# --- the claim mapping (scope_name IS the claim name ABS requests) ---------------
+mapping = ScopeMapping.objects.filter(name="audiobookshelf-groups").first()
+if mapping is None:
+    mapping = ScopeMapping.objects.create(name="audiobookshelf-groups", scope_name=CLAIM,
+                                          expression=EXPR,
+                                          description="Audiobookshelf role names from group membership")
+    print("mapping: created (scope_name %s)" % CLAIM)
+elif mapping.scope_name != CLAIM or mapping.expression != EXPR:
+    mapping.scope_name, mapping.expression = CLAIM, EXPR
+    mapping.save(update_fields=["scope_name", "expression"])
+    print("mapping: scope/expression updated (scope_name %s)" % CLAIM)
+else:
+    print("mapping: already current")
+
+# Prove the expression runs and yields an ABS role BEFORE anyone tries to log in:
+# authentik execs the expression inside a function whose context has `user`.
+_src = "def _probe(user, request=None):\n" + "".join("    %s\n" % ln for ln in EXPR.splitlines())
+_ns = {}
+exec(_src, _ns)
+
+# --- provider --------------------------------------------------------------------
+uris = [RedirectURI(matching_mode=RedirectURIMatchingMode.STRICT,
+                    url="%s/auth/openid/callback" % BASE),
+        RedirectURI(matching_mode=RedirectURIMatchingMode.STRICT,
+                    url="%s/auth/openid/mobile-redirect" % BASE)]
+authz_flow = Flow.objects.get(slug="default-provider-authorization-implicit-consent")
+
+p = OAuth2Provider.objects.filter(name="audiobookshelf").first()
+if p is None:
+    p = OAuth2Provider(name="audiobookshelf", client_id=CLIENT_ID,
+                       client_type=ClientType.CONFIDENTIAL, client_secret=SECRET,
+                       authorization_flow=authz_flow)
+    p.redirect_uris = uris
+    p.save()
+    p.property_mappings.set([mapping])
+    print("provider: created")
+else:
+    changed = []
+    if p.client_id != CLIENT_ID:
+        p.client_id = CLIENT_ID
+        changed.append("client_id")
+    if p.client_secret != SECRET:
+        p.client_secret = SECRET
+        changed.append("client_secret")
+    if p.authorization_flow_id != authz_flow.pk:
+        p.authorization_flow = authz_flow
+        changed.append("authorization_flow")
+    if [(u.url, str(u.matching_mode)) for u in p.redirect_uris] != \
+       [(u.url, str(u.matching_mode)) for u in uris]:
+        p.redirect_uris = uris
+        changed.append("redirect_uris")
+    if changed:
+        p.save()
+    if sorted(m.pk for m in p.property_mappings.all()) != [mapping.pk]:
+        p.property_mappings.set([mapping])
+        changed.append("property_mappings")
+    print("provider: asserted (%s)" % (", ".join(changed) or "nothing to change"))
+
+# --- application (the launchpad entry; binds the provider) ------------------------
+app = Application.objects.filter(slug="audiobookshelf").first()
+if app is None:
+    app = Application.objects.create(name="audiobookshelf", slug="audiobookshelf",
+                                     provider=p, meta_launch_url=BASE)
+    print("application: created")
+elif app.provider_id != p.pk or app.meta_launch_url != BASE:
+    app.provider, app.meta_launch_url = p, BASE
+    app.save(update_fields=["provider", "meta_launch_url"])
+    print("application: asserted")
+else:
+    print("application: already bound")
+
+# --- membership --------------------------------------------------------------------
+root = User.objects.get(username=SSO_USER)
+root.groups.add(admin_g)
+print("admin: %s in %s" % (SSO_USER, ADMIN_GROUP))
+for name in MEMBERS:
+    u = User.objects.get(username=name)
+    u.groups.add(user_g)
+print("users: %s in %s" % (", ".join(MEMBERS) or "(none — fail closed)", USER_GROUP))
+
+# --- verification: the claim the callback will actually receive ---------------------
+for probe in [root] + [User.objects.get(username=n) for n in MEMBERS]:
+    print("claim for %s -> %s" % (probe.username, _ns["_probe"](user=probe, request=None)))
+p.refresh_from_db()
+print("provider %s | client_id %s | flow %s | uris %s" % (
+    p.name, p.client_id, p.authorization_flow.slug, [u.url for u in p.redirect_uris]))
+PYEOF
+
+cat <<DONE
+
+Next: arm the Audiobookshelf side (issuer, client, HS256, claim) —
+  ssh dankserver 'ABS_OIDC=1 bash /home/dank/serverAppConfigs/scripts/audiobookshelf-init.sh'
+It reads the same secret from /home/dank/.config/secrets/audiobookshelf and verifies
+/status answers openid among its auth methods.
+DONE

tests/audiobookshelf_init.bats

@@ -17,6 +17,10 @@
 #      reported as success (a green deploy over a dead API is a lie);
 #   5. ABS_SCAN outside 0/1 is a usage error raised before anything is touched;
 #   6. the deployer runs the bootstrapper only after the health gate answered.
+#   7. the SSO arm sends the base path: ABS builds its redirect_uri as
+#      <origin><authOpenIDSubfolderForRedirectURLs>/auth/openid/callback, and the
+#      value must be the path the app is mounted under — never the literal
+#      "undefined" a fresh database leaves there.
 
 load helpers
 
@@ -29,7 +33,7 @@ import json, sys
 from http.server import BaseHTTPRequestHandler, ThreadingHTTPServer
 
 port, logf = int(sys.argv[1]), sys.argv[2]
-state = {"init": False, "user": None, "pw": None, "libs": []}
+state = {"init": False, "user": None, "pw": None, "libs": [], "oidc": None}
 
 
 def log(line):
@@ -37,6 +41,12 @@ def log(line):
         f.write(line + "\n")
 
 
+def norm(p):
+    # ABS mounts every route under ROUTER_BASE_PATH. The stub accepts the API at the
+    # root or under that prefix, so a test can still assert which one the client used.
+    return p[len("/audiobookshelf"):] if p.startswith("/audiobookshelf") else p
+
+
 class H(BaseHTTPRequestHandler):
     def log_message(self, *a):
         pass
@@ -57,20 +67,24 @@ class H(BaseHTTPRequestHandler):
         return self.headers.get("Authorization") == "Bearer stub-token"
 
     def do_GET(self):
-        path = self.path.split("?")[0]
+        path = norm(self.path.split("?")[0])
         log("GET %s auth=%s" % (self.path, "yes" if self.headers.get("Authorization") else "no"))
         if path == "/status":
-            return self.send(200, {"app": "audiobookshelf", "isInit": state["init"]}, True)
+            methods = ["local", "openid"] if state["oidc"] else ["local"]
+            return self.send(200, {"app": "audiobookshelf", "isInit": state["init"],
+                                   "authMethods": methods}, True)
         if not self.authed():
             return self.send(401, "Unauthorized")
         if path == "/api/libraries":
             return self.send(200, {"libraries": state["libs"]}, True)
+        if path == "/api/auth-settings":
+            return self.send(200, state["oidc"] or {}, True)
         if path.endswith("/items"):
             return self.send(200, {"total": 42, "results": []}, True)
         return self.send(404, "nope")
 
     def do_POST(self):
-        path = self.path.split("?")[0]
+        path = norm(self.path.split("?")[0])
         payload = self.body()
         log("POST %s auth=%s" % (self.path, "yes" if self.headers.get("Authorization") else "no"))
         if path == "/init":
@@ -101,6 +115,21 @@ class H(BaseHTTPRequestHandler):
             return self.send(200, "OK")
         return self.send(404, "nope")
 
+    def do_PATCH(self):
+        path = norm(self.path.split("?")[0])
+        payload = self.body()
+        log("PATCH %s auth=%s" % (self.path, "yes" if self.headers.get("Authorization") else "no"))
+        if not self.authed():
+            return self.send(401, "Unauthorized")
+        if path == "/api/auth-settings":
+            # Stored and echoed verbatim: the test asserts the wire, not the stub's
+            # opinion about which keys are patchable.
+            state["oidc"] = payload
+            for k in sorted(payload):
+                log("OIDCFG %s=%r" % (k, payload[k]))
+            return self.send(200, payload, True)
+        return self.send(404, "nope")
+
 
 ThreadingHTTPServer(("127.0.0.1", port), H).serve_forever()
 PY
@@ -198,3 +227,50 @@ boot() {
         /audiobookshelf-init\.sh/        { init = NR }
         END { exit !(health && init && init > health) }'
 }
+
+@test "the SSO arm sends the base path as the redirect subfolder" {
+    # What authentik has registered must equal what ABS builds:
+    # <origin><authOpenIDSubfolderForRedirectURLs>/auth/openid/callback. A database
+    # created before SSO leaves that key unset and ABS then sends the literal
+    # "/undefined/auth/openid/callback" — measured 2026-11-02, where the live login died
+    # on authentik's "Redirect URI Error" page. So the value has to reach the wire, and
+    # it has to be the path the app is served under.
+    umask 077
+    cat > "$TMP/cred" <<'CRED'
+ABS_ADMIN_USER=frank
+ABS_ADMIN_PASSWORD=0123456789abcdef0123456789
+ABS_OIDC_CLIENT_SECRET=0123456789abcdef0123456789abcdef0123456789abcdef0123456789
+CRED
+    run env ABS_URL="http://127.0.0.1:$PORT/audiobookshelf" ABS_SECRET="$TMP/cred" \
+        ABS_SCAN=0 bash "$INIT"
+    [ "$status" -eq 0 ]
+    printf '%s\n' "${lines[@]}" | grep -q "^oidc: armed"
+    grep -q "^OIDCFG authOpenIDSubfolderForRedirectURLs='/audiobookshelf'$" "$TMP/requests.log"
+    # every route the bootstrapper calls rides under the same prefix it armed with
+    grep -q "^POST /audiobookshelf/init auth=no$" "$TMP/requests.log"
+    grep -q "^GET /audiobookshelf/api/auth-settings auth=yes$" "$TMP/requests.log"
+
+    # A root-mounted deployment sends the EMPTY subfolder (the value the 2.17.4 upgrade
+    # uses), not whatever the last URL happened to carry.
+    run env ABS_URL="http://127.0.0.1:$PORT" ABS_SECRET="$TMP/cred" ABS_SCAN=0 bash "$INIT"
+    [ "$status" -eq 0 ]
+    [ "$(grep "^OIDCFG authOpenIDSubfolderForRedirectURLs=" "$TMP/requests.log" | tail -1)" \
+        = "OIDCFG authOpenIDSubfolderForRedirectURLs=''" ]
+}
+
+@test "the app and the IdP provider script build the same redirect path" {
+    # The provider row is written by scripts/authentik-audiobookshelf-sso.sh from
+    # ABS_BASE; the app builds its redirect_uri from the base path the deployer hands
+    # audiobookshelf-init.sh, which comes from the unit. Drift between the two is a
+    # redirect_uri mismatch — the login dies at the IdP before any credential is issued.
+    unit="$REPO_ROOT/dankserver/audiobookshelf/quadlet/audiobookshelf.container"
+    mounted=$(awk -F= '/^Environment=ROUTER_BASE_PATH=/{print $3}' "$unit")
+    [ -n "$mounted" ]
+    provider=$(grep -m1 '^BASE=' "$REPO_ROOT/scripts/authentik-audiobookshelf-sso.sh" \
+        | grep -oE 'https?://[^"}]+')
+    bootstrapper=$(grep -m1 '^ABS_URL=' "$INIT" | grep -oE 'https?://[^"}]+')
+    # Origins legitimately differ (LAN address vs loopback); the PATH must not.
+    [ "${provider#http://192.168.0.235:8000}/auth/openid/callback" \
+        = "${bootstrapper#http://127.0.0.1:8000}/auth/openid/callback" ]
+    [ "${bootstrapper#http://127.0.0.1:8000}" = "$mounted" ]
+}