feat(auth): login-guard the Furtka UI with a cookie session

One-admin, one-password model — all of /apps, /api/*, /, and
/settings/ now require a signed-in session. Passwords are werkzeug
PBKDF2-hashed in /var/lib/furtka/users.json (mode 0600, atomic write
via the same .tmp+chmod+rename dance installer.write_env uses).
Sessions are secrets.token_urlsafe(32) tokens held in a module-level
SessionStore dict (thread-safe lock included for when we swap to
ThreadingHTTPServer). Cookies are HttpOnly, SameSite=Strict, and
Path=/, with Secure set when X-Forwarded-Proto from Caddy says HTTPS.

Two bootstrap paths:
  * Fresh install — webinstaller step-1 collects Linux user + password,
    the chroot post-install step hashes the password and writes
    users.json on the target partition. First browser visit lands on
    /login with the account already present.
  * Upgrade from 26.10-alpha — no users.json yet, so /login detects
    setup_needed() and renders a first-run setup form. POST creates
    the admin and immediately logs in.

POST /logout revokes the server session and clears the cookie.
Unauthenticated HTML requests 302 to /login; unauthenticated API
requests 401 JSON so fetch() callers see a clean error. A sleep(0.5)
on failed logins is the brute-force speed bump on top of werkzeug's
~600k-iter PBKDF2.

Caddyfile gains /login* and /logout* handle blocks in the shared
furtka_routes snippet so both :80 and the HTTPS hostname block
forward the auth endpoints to localhost:7000. Without this Caddy
would 404 from the static file server.

Test surface:
  * tests/test_auth.py (new, 19 cases): hash roundtrip, users.json
    I/O, session create/lookup/expire/revoke.
  * tests/test_api.py: new admin_session fixture; existing HTTP
    tests updated to send the cookie; new tests cover login setup,
    login success, wrong-password 401, logout revocation, and the
    guard's 302/401 split.
  * tests/test_webinstaller_assets.py: new case that unpacks the
    users.json _write_file_cmd body and verifies the werkzeug hash
    round-trips against the step-1 password.

Bumped version to 26.11-alpha and rolled CHANGELOG. Also folded in
the ruff-format fix that was pending from 26.10-alpha's lint red.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

CHANGELOG.md

@@ -7,6 +7,46 @@ This project uses calendar versioning: `YY.N-stage` (e.g. `26.0-alpha` = 2026, r
 
 ## [Unreleased]
 
+## [26.11-alpha] - 2026-04-21
+
+### Added
+
+- **Login-auth for the Furtka web UI.** Every `/apps`, `/api/*`, `/`,
+  and `/settings/` route now requires a signed-in session. New
+  `/login` page serves a username/password form; `POST /login`
+  validates against `/var/lib/furtka/users.json` (werkzeug PBKDF2-
+  hashed), sets a `furtka_session` cookie (`HttpOnly`, `SameSite=
+  Strict`, 7-day TTL), and redirects to `/apps`. `POST /logout`
+  revokes the server-side session and clears the cookie.
+  Unauthenticated HTML requests get a 302 to `/login`; unauthenticated
+  API requests get 401 JSON. The old "No authentication on this UI
+  yet" banner is gone; the `/apps` header picks up a `Logout` link
+  instead.
+- **First-run setup fallback for upgrade-path boxes.** Boxes
+  upgrading from 26.10-alpha have no `users.json` yet — on the first
+  visit `/login` renders a setup form (username + password +
+  password-confirm) that creates the admin record on submit. Fresh
+  installs skip this: the webinstaller writes `users.json` during
+  the chroot post-install step using the step-1 password, so the
+  first browser visit after boot goes straight to the login form.
+- **Caddy proxy routes `/login` and `/logout`.** `assets/Caddyfile`
+  gets two new `handle` blocks in the shared `(furtka_routes)`
+  snippet so both the `:80` block and the `hostname.local, hostname`
+  HTTPS block forward the auth endpoints to the stdlib server on
+  `127.0.0.1:7000`. Without this Caddy would serve a 404 from the
+  static file server.
+
+### Fixed
+
+- `tests/test_installer.py` ruff-format nit — the 26.10-alpha
+  release commit had a misformatted list literal that failed
+  `ruff format --check`. Caught when the Release page on Forgejo
+  showed a red CI badge for the tag.
+- `pyproject.toml` version string bumped from the stale 26.8-alpha
+  to 26.11-alpha. Release pipeline uses `GITHUB_REF_NAME` as source
+  of truth for the artefact name, but having the two agree matters
+  for local dev runs that read `pyproject.toml`.
+
 ## [26.10-alpha] - 2026-04-21
 
 ### Added
@@ -182,7 +222,8 @@ First tagged snapshot. Pre-alpha — the installer does not yet boot, but the de
 - **Containers:** Docker + Compose
 - **License:** AGPL-3.0
 
-[Unreleased]: https://forgejo.sourcegate.online/daniel/furtka/compare/26.10-alpha...HEAD
+[Unreleased]: https://forgejo.sourcegate.online/daniel/furtka/compare/26.11-alpha...HEAD
+[26.11-alpha]: https://forgejo.sourcegate.online/daniel/furtka/releases/tag/26.11-alpha
 [26.10-alpha]: https://forgejo.sourcegate.online/daniel/furtka/releases/tag/26.10-alpha
 [26.9-alpha]: https://forgejo.sourcegate.online/daniel/furtka/releases/tag/26.9-alpha
 [26.8-alpha]: https://forgejo.sourcegate.online/daniel/furtka/releases/tag/26.8-alpha

assets/Caddyfile

@@ -35,6 +35,12 @@
 	handle /apps* {
 		reverse_proxy localhost:7000
 	}
+	handle /login* {
+		reverse_proxy localhost:7000
+	}
+	handle /logout* {
+		reverse_proxy localhost:7000
+	}
 	# Runtime JSON lives under /var/lib/furtka/ so it survives self-updates
 	# (which only swap /opt/furtka/current).
 	handle /status.json {

assets/www/style.css

@@ -310,7 +310,8 @@ details.log-details[open] > summary { color: var(--fg); }
 }
 .field input:focus { outline: 2px solid var(--accent); outline-offset: -1px; }
 .field .req { color: var(--danger); margin-left: 0.25rem; }
-.modal .error {
+.modal .error,
+.login-wrap .error {
     background: var(--warn);
     color: var(--warn-fg);
     padding: 0.5rem 0.75rem;
@@ -319,7 +320,15 @@ details.log-details[open] > summary { color: var(--fg); }
     font-size: 0.9rem;
     display: none;
 }
-.modal .error.show { display: block; }
+.modal .error.show,
+.login-wrap .error.show { display: block; }
+
+/* Login + first-run setup page. Shares .wrap's max-width so the form
+   sits in the same column the rest of the app uses, just without the
+   Home/Apps/Settings nav. A bit of top padding so the H1 isn't glued
+   to the viewport edge. */
+.login-wrap { padding-top: 3rem; }
+.login-wrap .actions { margin-top: 0.5rem; }
 .modal-actions {
     display: flex;
     justify-content: flex-end;

furtka/api.py

@@ -2,20 +2,26 @@
 # its lines hurts readability and the rendered output is what matters here.
 """Tiny HTTP API + management UI for the Furtka resource manager.
 
-Single stdlib http.server process, no Flask/no third-party deps so we don't
-have to pip-install anything on the target. Caddy reverse-proxies /apps and
-/api from :80 to here.
+Single stdlib http.server process, served behind Caddy (reverse-proxies
+/apps, /api, /login and /logout from :80 to here).
 
-Security: NO AUTH. Bound to 127.0.0.1 by default; the Caddy proxy makes it
-LAN-reachable. Anyone on the LAN can install/remove apps. The UI shouts this
-out at the top. Auth lands when Authentik does.
+Security: single-admin password login, cookie-session, werkzeug-hashed
+password stored at /var/lib/furtka/users.json (0600). Sessions live in
+memory — `systemctl restart furtka-api` invalidates everyone. Fresh
+installs pre-populate users.json from the webinstaller step-1 password;
+upgrades from pre-auth releases fall into a first-run setup form at
+/login where the admin password is created from the browser. Authentik
+integration remains the long-term plan; this is the pragmatic alpha
+stopgap.
 """
 
 import json
 import re
+import time
+from http.cookies import SimpleCookie
 from http.server import BaseHTTPRequestHandler, HTTPServer
 
-from furtka import dockerops, installer, reconciler, sources
+from furtka import auth, dockerops, installer, reconciler, sources
 from furtka.manifest import ManifestError, load_manifest
 from furtka.paths import apps_dir
 from furtka.scanner import scan
@@ -77,12 +83,12 @@ _HTML = """<!DOCTYPE html>
         <a href="/">Home</a>
         <a href="/apps" aria-current="page">Apps</a>
         <a href="/settings/">Settings</a>
+        <a href="#" id="logout-link" onclick="return doLogout(event)">Logout</a>
       </div>
     </nav>
 
     <h1>Furtka Apps</h1>
     <p class="lede">Install or remove resource-manager apps on this Furtka box.</p>
-    <div class="warn">No authentication on this UI yet. Anyone on your LAN can install or remove apps. Don't expose this to the wider internet.</div>
 
     <h2>Installed</h2>
     <div id="installed"></div>
@@ -120,6 +126,15 @@ function esc(s) {
   return d.innerHTML;
 }
 
+async function doLogout(ev) {
+  ev.preventDefault();
+  try {
+    await fetch('/logout', { method: 'POST', credentials: 'same-origin' });
+  } catch (e) { /* best-effort — server may already be down */ }
+  window.location.href = '/login';
+  return false;
+}
+
 // Fallback when an app doesn't ship a parseable icon.svg. Simple
 // stroked folder — currentColor so the tile's accent tint applies.
 const FALLBACK_ICON = '<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="1.5" stroke-linecap="round" stroke-linejoin="round"><path d="M3 7v12a2 2 0 0 0 2 2h14a2 2 0 0 0 2-2V9a2 2 0 0 0-2-2h-7l-2-2H5a2 2 0 0 0-2 2z"/></svg>';
@@ -387,6 +402,120 @@ refreshCatalog();
 """
 
 
+# Login / first-run setup page. Rendered standalone (no main-UI chrome) so
+# an unauthenticated visitor never gets a glimpse of the app list. Reuses
+# /style.css for the look — the page is just a form + optional error line.
+# The template has a {{ SETUP }} marker the server flips on/off depending
+# on whether users.json exists yet (first-run vs. normal login).
+_HTML_LOGIN = """<!DOCTYPE html>
+<html lang="en">
+<head>
+<meta charset="utf-8">
+<title>Furtka · {{ TITLE }}</title>
+<meta name="viewport" content="width=device-width,initial-scale=1">
+<link rel="stylesheet" href="/style.css">
+</head>
+<body>
+  <main class="wrap login-wrap">
+    <h1>{{ HEADING }}</h1>
+    <p class="lede">{{ LEDE }}</p>
+    <form id="login-form" onsubmit="return doLogin(event)">
+      <div class="field">
+        <label for="username">Username</label>
+        <input id="username" name="username" type="text" autocomplete="username" required value="{{ DEFAULT_USERNAME }}" autofocus>
+      </div>
+      <div class="field">
+        <label for="password">Password</label>
+        <input id="password" name="password" type="password" autocomplete="{{ PWD_AUTOCOMPLETE }}" required minlength="8">
+      </div>
+      {{ PASSWORD2_FIELD }}
+      <div id="login-error" class="error"></div>
+      <div class="actions">
+        <button type="submit" id="login-submit">{{ SUBMIT_LABEL }}</button>
+      </div>
+    </form>
+  </main>
+<script>
+const SETUP = {{ SETUP_JSON }};
+const errBox = document.getElementById('login-error');
+async function doLogin(ev) {
+  ev.preventDefault();
+  errBox.classList.remove('show');
+  errBox.textContent = '';
+  const btn = document.getElementById('login-submit');
+  btn.disabled = true;
+  const body = {
+    username: document.getElementById('username').value,
+    password: document.getElementById('password').value,
+  };
+  if (SETUP) body.password2 = document.getElementById('password2').value;
+  try {
+    const r = await fetch('/login', {
+      method: 'POST',
+      headers: {'Content-Type': 'application/json'},
+      credentials: 'same-origin',
+      body: JSON.stringify(body),
+    });
+    if (r.ok) {
+      window.location.href = '/apps';
+      return false;
+    }
+    const data = await r.json().catch(() => ({error: 'HTTP ' + r.status}));
+    errBox.textContent = data.error || 'Login failed';
+    errBox.classList.add('show');
+  } catch (e) {
+    errBox.textContent = 'Network error — is the box reachable?';
+    errBox.classList.add('show');
+  } finally {
+    btn.disabled = false;
+  }
+  return false;
+}
+</script>
+</body>
+</html>
+"""
+
+
+def _render_login_html(setup: bool, default_username: str = "") -> str:
+    if setup:
+        password2_field = (
+            '<div class="field"><label for="password2">Repeat password</label>'
+            '<input id="password2" name="password2" type="password" '
+            'autocomplete="new-password" required minlength="8"></div>'
+        )
+        subs = {
+            "TITLE": "First-run setup",
+            "HEADING": "Set admin password",
+            "LEDE": "No admin account exists yet on this box. Pick a username and password — you'll use them to sign in to the Furtka UI.",
+            "PWD_AUTOCOMPLETE": "new-password",
+            "PASSWORD2_FIELD": password2_field,
+            "SUBMIT_LABEL": "Create admin",
+            "DEFAULT_USERNAME": "admin",
+            "SETUP_JSON": "true",
+        }
+    else:
+        subs = {
+            "TITLE": "Login",
+            "HEADING": "Furtka login",
+            "LEDE": "Sign in with the admin credentials you set during install.",
+            "PWD_AUTOCOMPLETE": "current-password",
+            "PASSWORD2_FIELD": "",
+            "SUBMIT_LABEL": "Log in",
+            "DEFAULT_USERNAME": default_username,
+            "SETUP_JSON": "false",
+        }
+    out = _HTML_LOGIN
+    for key, val in subs.items():
+        out = out.replace("{{ " + key + " }}", val)
+    return out
+
+
+# Minimum password length enforced server-side (browser also enforces it
+# via the input's minlength, but don't rely on client-side only).
+_MIN_PASSWORD_LEN = 8
+
+
 def _manifest_summary(m, app_dir=None):
     return {
         "name": m.name,
@@ -826,23 +955,134 @@ def _parse_settings_body(payload):
 
 
 class _Handler(BaseHTTPRequestHandler):
-    def _json(self, status, payload):
+    def _json(self, status, payload, extra_headers=None):
         body = json.dumps(payload).encode()
         self.send_response(status)
         self.send_header("Content-Type", "application/json")
         self.send_header("Content-Length", str(len(body)))
+        for name, value in extra_headers or []:
+            self.send_header(name, value)
         self.end_headers()
         self.wfile.write(body)
 
-    def _html(self, status, body):
+    def _html(self, status, body, extra_headers=None):
         b = body.encode()
         self.send_response(status)
         self.send_header("Content-Type", "text/html; charset=utf-8")
         self.send_header("Content-Length", str(len(b)))
+        for name, value in extra_headers or []:
+            self.send_header(name, value)
         self.end_headers()
         self.wfile.write(b)
 
+    def _redirect(self, location, extra_headers=None):
+        self.send_response(302)
+        self.send_header("Location", location)
+        self.send_header("Content-Length", "0")
+        for name, value in extra_headers or []:
+            self.send_header(name, value)
+        self.end_headers()
+
+    # ---- Auth helpers -------------------------------------------------
+
+    def _request_cookies(self) -> SimpleCookie:
+        cookies = SimpleCookie()
+        header = self.headers.get("Cookie")
+        if header:
+            try:
+                cookies.load(header)
+            except Exception:
+                # Malformed Cookie header — treat as no cookies rather
+                # than 500ing. Same posture as browsers.
+                return SimpleCookie()
+        return cookies
+
+    def _current_session(self):
+        cookies = self._request_cookies()
+        morsel = cookies.get(auth.COOKIE_NAME)
+        if morsel is None:
+            return None
+        return auth.SESSIONS.lookup(morsel.value)
+
+    def _session_cookie_header(self, token: str, max_age: int) -> tuple[str, str]:
+        secure = self.headers.get("X-Forwarded-Proto", "").lower() == "https"
+        parts = [
+            f"{auth.COOKIE_NAME}={token}",
+            "HttpOnly",
+            "SameSite=Strict",
+            "Path=/",
+            f"Max-Age={max_age}",
+        ]
+        if secure:
+            parts.append("Secure")
+        return ("Set-Cookie", "; ".join(parts))
+
+    def _clear_cookie_header(self) -> tuple[str, str]:
+        # Max-Age=0 with an empty value tells the browser to drop it.
+        return (
+            "Set-Cookie",
+            f"{auth.COOKIE_NAME}=; HttpOnly; SameSite=Strict; Path=/; Max-Age=0",
+        )
+
+    def _handle_login(self, payload):
+        username = payload.get("username") if isinstance(payload, dict) else None
+        password = payload.get("password") if isinstance(payload, dict) else None
+        if not isinstance(username, str) or not username.strip():
+            return self._json(400, {"error": "username is required"})
+        if not isinstance(password, str) or not password:
+            return self._json(400, {"error": "password is required"})
+        username = username.strip()
+
+        if auth.setup_needed():
+            # First-run setup path — create the admin account, then log
+            # in. Require password2 so a typo doesn't lock the user out
+            # of their own box.
+            password2 = payload.get("password2")
+            if password2 != password:
+                return self._json(400, {"error": "passwords do not match"})
+            if len(password) < _MIN_PASSWORD_LEN:
+                return self._json(
+                    400,
+                    {"error": f"password must be at least {_MIN_PASSWORD_LEN} characters"},
+                )
+            auth.create_admin(username, password)
+        else:
+            if not auth.authenticate(username, password):
+                # Cheap brute-force speed bump. werkzeug's PBKDF2 is
+                # already slow per attempt, but a fixed sleep makes
+                # "try 1000 passwords over the LAN" even less fun.
+                time.sleep(0.5)
+                return self._json(401, {"error": "invalid username or password"})
+
+        session = auth.SESSIONS.create(username)
+        cookie = self._session_cookie_header(session.token, auth.COOKIE_TTL_SECONDS)
+        return self._json(200, {"ok": True, "username": username}, extra_headers=[cookie])
+
+    def _handle_logout(self):
+        cookies = self._request_cookies()
+        morsel = cookies.get(auth.COOKIE_NAME)
+        if morsel is not None:
+            auth.SESSIONS.revoke(morsel.value)
+        return self._json(200, {"ok": True}, extra_headers=[self._clear_cookie_header()])
+
     def do_GET(self):  # noqa: N802 — http.server convention
+        # --- Public routes: login page + its assets ------------------
+        if self.path in ("/login", "/login/"):
+            # Already authed? Skip straight to the app list.
+            if self._current_session() is not None:
+                return self._redirect("/apps")
+            return self._html(200, _render_login_html(auth.setup_needed()))
+
+        # --- Auth guard for everything below -------------------------
+        session = self._current_session()
+        if session is None:
+            # API paths get a 401 JSON so fetch() callers see a clean
+            # error. HTML paths get a redirect to /login so the browser
+            # naturally ends up on the login form.
+            if self.path.startswith("/api/"):
+                return self._json(401, {"error": "not authenticated"})
+            return self._redirect("/login")
+
         if self.path in ("/", "/apps", "/apps/"):
             return self._html(200, _HTML)
         if self.path == "/api/apps":
@@ -879,6 +1119,16 @@ class _Handler(BaseHTTPRequestHandler):
         if not isinstance(payload, dict):
             return self._json(400, {"error": "body must be a JSON object"})
 
+        # --- Public routes: login + logout ----------------------------
+        if self.path in ("/login", "/login/"):
+            return self._handle_login(payload)
+        if self.path in ("/logout", "/logout/"):
+            return self._handle_logout()
+
+        # --- Auth guard for every other POST --------------------------
+        if self._current_session() is None:
+            return self._json(401, {"error": "not authenticated"})
+
         # Per-app settings update: /api/apps/<name>/settings
         if self.path.startswith("/api/apps/") and self.path.endswith("/settings"):
             name = self.path[len("/api/apps/") : -len("/settings")]

furtka/auth.py

@@ -0,0 +1,175 @@
+"""Login-guard primitives for the Furtka UI.
+
+One admin, one password. Passwords are PBKDF2-hashed via werkzeug (already
+pulled in by the flask runtime dep), stored in /var/lib/furtka/users.json
+with mode 0600. Sessions live in memory — a systemctl restart logs
+everyone out again, which is fine for an alpha single-user box.
+
+On upgrade from 26.10-alpha the users.json file does not exist yet; the
+api's GET /login detects this via `setup_needed()` and renders a first-
+run form that POSTs to /login as if it were a setup submit. Fresh installs
+get the file pre-populated by the webinstaller so the setup step is
+skipped.
+"""
+
+from __future__ import annotations
+
+import json
+import secrets
+import threading
+from dataclasses import dataclass
+from datetime import UTC, datetime, timedelta
+
+from werkzeug.security import check_password_hash, generate_password_hash
+
+from furtka.paths import users_file
+
+COOKIE_NAME = "furtka_session"
+COOKIE_TTL_SECONDS = 7 * 24 * 3600  # one week
+
+
+def hash_password(plain: str) -> str:
+    """PBKDF2-SHA256 via werkzeug. Cost default (~600k iterations)."""
+    return generate_password_hash(plain)
+
+
+def verify_password(plain: str, hashed: str) -> bool:
+    # werkzeug's check_password_hash is constant-time.
+    return check_password_hash(hashed, plain)
+
+
+def load_users() -> dict:
+    """Return the users dict, or {} if the file is missing or empty.
+
+    Missing-file is the expected state on first boot and on upgrades from
+    pre-auth versions — callers treat empty-dict as "setup required".
+    """
+    path = users_file()
+    if not path.exists():
+        return {}
+    try:
+        raw = path.read_text()
+    except OSError:
+        return {}
+    if not raw.strip():
+        return {}
+    try:
+        data = json.loads(raw)
+    except json.JSONDecodeError:
+        return {}
+    if not isinstance(data, dict):
+        return {}
+    return data
+
+
+def save_users(users: dict) -> None:
+    """Atomically write users.json with mode 0600.
+
+    Same pattern as installer.write_env — write to .tmp, chmod, rename —
+    so a crash between open() and close() can't leave a world-readable
+    partial file.
+    """
+    path = users_file()
+    path.parent.mkdir(parents=True, exist_ok=True)
+    tmp = path.with_suffix(path.suffix + ".tmp")
+    tmp.write_text(json.dumps(users, indent=2) + "\n")
+    tmp.chmod(0o600)
+    tmp.replace(path)
+
+
+def setup_needed() -> bool:
+    """True when no admin is registered yet — initial setup is required."""
+    users = load_users()
+    return not users or "admin" not in users
+
+
+def create_admin(username: str, password: str) -> None:
+    """Overwrite users.json with a single admin account.
+
+    The webinstaller calls this post-install (with the step-1 password) so
+    the installed system is login-guarded from first boot. The /login
+    route calls it on first setup for upgrade-path boxes that don't
+    already have a users.json.
+    """
+    users = {
+        "admin": {
+            "username": username,
+            "hash": hash_password(password),
+            "created_at": datetime.now(UTC).isoformat(timespec="seconds"),
+        }
+    }
+    save_users(users)
+
+
+def authenticate(username: str, password: str) -> bool:
+    """Return True iff the supplied credentials match the admin record."""
+    users = load_users()
+    admin = users.get("admin")
+    if not admin:
+        return False
+    if admin.get("username") != username:
+        return False
+    hashed = admin.get("hash")
+    if not isinstance(hashed, str) or not hashed:
+        return False
+    return verify_password(password, hashed)
+
+
+@dataclass(frozen=True)
+class Session:
+    token: str
+    username: str
+    expires_at: datetime
+
+
+class SessionStore:
+    """In-memory session table. Thread-safe (api.py uses the stdlib
+
+    HTTPServer which handles one request per thread — though the default
+    variant is single-threaded, we keep the lock so swapping to
+    ThreadingHTTPServer later doesn't require revisiting this).
+    """
+
+    def __init__(self, ttl_seconds: int = COOKIE_TTL_SECONDS) -> None:
+        self._ttl = timedelta(seconds=ttl_seconds)
+        self._by_token: dict[str, Session] = {}
+        self._lock = threading.Lock()
+
+    def create(self, username: str) -> Session:
+        token = secrets.token_urlsafe(32)
+        session = Session(
+            token=token,
+            username=username,
+            expires_at=datetime.now(UTC) + self._ttl,
+        )
+        with self._lock:
+            self._by_token[token] = session
+        return session
+
+    def lookup(self, token: str | None) -> Session | None:
+        if not token:
+            return None
+        with self._lock:
+            session = self._by_token.get(token)
+            if session is None:
+                return None
+            if datetime.now(UTC) >= session.expires_at:
+                # Expired — drop it on the floor so repeat lookups stay fast.
+                self._by_token.pop(token, None)
+                return None
+            return session
+
+    def revoke(self, token: str | None) -> None:
+        if not token:
+            return
+        with self._lock:
+            self._by_token.pop(token, None)
+
+    def clear(self) -> None:
+        """Test helper — wipe all sessions."""
+        with self._lock:
+            self._by_token.clear()
+
+
+# Module-level singleton used by the HTTP handler.
+SESSIONS = SessionStore()

furtka/paths.py

@@ -11,6 +11,11 @@ DEFAULT_BUNDLED_APPS_DIR = Path("/opt/furtka/current/apps")
 # release tarball. Lives under /var/lib/furtka/ so it survives core self-
 # updates — the resolver (furtka.sources) prefers it over the bundled seed.
 DEFAULT_CATALOG_DIR = Path("/var/lib/furtka/catalog")
+# Users / auth state. One JSON file keyed by role — today only "admin" exists.
+# Lives under /var/lib/furtka/ so self-updates don't stomp it. Mode 0600 is
+# enforced by furtka.auth.save_users (same atomic-write pattern as the app
+# .env files).
+DEFAULT_USERS_FILE = Path("/var/lib/furtka/users.json")
 
 
 def apps_dir() -> Path:
@@ -27,3 +32,7 @@ def catalog_dir() -> Path:
 
 def catalog_apps_dir() -> Path:
     return catalog_dir() / "apps"
+
+
+def users_file() -> Path:
+    return Path(os.environ.get("FURTKA_USERS_FILE", DEFAULT_USERS_FILE))

pyproject.toml

@@ -1,6 +1,6 @@
 [project]
 name = "furtka"
-version = "26.8-alpha"
+version = "26.11-alpha"
 description = "Open-source home server OS — simple enough for everyone."
 requires-python = ">=3.11"
 readme = "README.md"

tests/test_api.py

@@ -5,7 +5,7 @@ import urllib.request
 
 import pytest
 
-from furtka import api, dockerops
+from furtka import api, auth, dockerops
 
 VALID_MANIFEST = {
     "name": "fileshare",
@@ -23,14 +23,28 @@ def fake_dirs(tmp_path, monkeypatch):
     apps = tmp_path / "apps"
     bundled = tmp_path / "bundled"
     catalog = tmp_path / "catalog"
+    users_file = tmp_path / "users.json"
     apps.mkdir()
     bundled.mkdir()
     monkeypatch.setenv("FURTKA_APPS_DIR", str(apps))
     monkeypatch.setenv("FURTKA_BUNDLED_APPS_DIR", str(bundled))
     monkeypatch.setenv("FURTKA_CATALOG_DIR", str(catalog))
+    monkeypatch.setenv("FURTKA_USERS_FILE", str(users_file))
+    # Scrub any sessions that leaked from a prior test — the SESSIONS
+    # store is module-level.
+    auth.SESSIONS.clear()
     return apps, bundled
 
 
+@pytest.fixture
+def admin_session(fake_dirs):
+    """Pre-create an admin account + live session. Returns a Cookie header
+    value ready to drop into urllib.request.Request(headers=...)."""
+    auth.create_admin("daniel", "hunter2-pw")
+    session = auth.SESSIONS.create("daniel")
+    return f"{auth.COOKIE_NAME}={session.token}"
+
+
 @pytest.fixture
 def no_docker(monkeypatch):
     """Stub docker calls so install/remove can run without a daemon."""
@@ -199,23 +213,39 @@ def test_remove_endpoint_happy_path(fake_dirs, no_docker):
     assert not (apps / "fileshare").exists()
 
 
-def test_http_get_apps_route(fake_dirs, no_docker):
+def _request(port, path, cookie=None, method="GET", body=None):
+    headers = {}
+    if cookie is not None:
+        headers["Cookie"] = cookie
+    data = None
+    if body is not None:
+        headers["Content-Type"] = "application/json"
+        data = json.dumps(body).encode()
+    return urllib.request.Request(
+        f"http://127.0.0.1:{port}{path}",
+        data=data,
+        headers=headers,
+        method=method,
+    )
+
+
+def test_http_get_apps_route(fake_dirs, no_docker, admin_session):
     """Smoke test the actual HTTP server with a real socket, urllib client."""
     server = api.HTTPServer(("127.0.0.1", 0), api._Handler)  # port 0 → ephemeral
     port = server.server_address[1]
     t = threading.Thread(target=server.serve_forever, daemon=True)
     t.start()
     try:
-        with urllib.request.urlopen(f"http://127.0.0.1:{port}/api/apps") as r:
+        with urllib.request.urlopen(_request(port, "/api/apps", cookie=admin_session)) as r:
             assert r.status == 200
             data = json.loads(r.read())
             assert data == []
-        with urllib.request.urlopen(f"http://127.0.0.1:{port}/") as r:
+        with urllib.request.urlopen(_request(port, "/", cookie=admin_session)) as r:
             assert r.status == 200
             assert b"Furtka Apps" in r.read()
         # Unknown route → 404 JSON.
         try:
-            urllib.request.urlopen(f"http://127.0.0.1:{port}/api/nope")
+            urllib.request.urlopen(_request(port, "/api/nope", cookie=admin_session))
             raise AssertionError("expected 404")
         except urllib.error.HTTPError as e:
             assert e.code == 404
@@ -224,17 +254,18 @@ def test_http_get_apps_route(fake_dirs, no_docker):
         server.server_close()
 
 
-def test_http_post_install_unknown_app(fake_dirs):
+def test_http_post_install_unknown_app(fake_dirs, admin_session):
     server = api.HTTPServer(("127.0.0.1", 0), api._Handler)
     port = server.server_address[1]
     t = threading.Thread(target=server.serve_forever, daemon=True)
     t.start()
     try:
-        req = urllib.request.Request(
-            f"http://127.0.0.1:{port}/api/apps/install",
-            data=json.dumps({"name": "ghost"}).encode(),
-            headers={"Content-Type": "application/json"},
+        req = _request(
+            port,
+            "/api/apps/install",
+            cookie=admin_session,
             method="POST",
+            body={"name": "ghost"},
         )
         try:
             urllib.request.urlopen(req)
@@ -248,6 +279,247 @@ def test_http_post_install_unknown_app(fake_dirs):
         server.server_close()
 
 
+# --- Auth guard + login flow ------------------------------------------------
+
+
+def _start_server():
+    server = api.HTTPServer(("127.0.0.1", 0), api._Handler)
+    port = server.server_address[1]
+    t = threading.Thread(target=server.serve_forever, daemon=True)
+    t.start()
+    return server, port
+
+
+def test_unauthenticated_api_returns_401(fake_dirs):
+    # No admin_session fixture → no cookie on the request.
+    server, port = _start_server()
+    try:
+        try:
+            urllib.request.urlopen(_request(port, "/api/apps"))
+            raise AssertionError("expected 401")
+        except urllib.error.HTTPError as e:
+            assert e.code == 401
+            body = json.loads(e.read())
+            assert body["error"] == "not authenticated"
+    finally:
+        server.shutdown()
+        server.server_close()
+
+
+def test_unauthenticated_html_redirects_to_login(fake_dirs):
+    server, port = _start_server()
+    try:
+        # Disable redirect following so we can inspect the 302.
+        opener = urllib.request.build_opener(_NoRedirectHandler())
+        try:
+            opener.open(_request(port, "/apps"))
+            raise AssertionError("expected 302")
+        except urllib.error.HTTPError as e:
+            assert e.code == 302
+            assert e.headers["Location"] == "/login"
+    finally:
+        server.shutdown()
+        server.server_close()
+
+
+class _NoRedirectHandler(urllib.request.HTTPRedirectHandler):
+    def redirect_request(self, *args, **kwargs):
+        return None
+
+
+def test_get_login_renders_login_form_when_admin_exists(fake_dirs):
+    auth.create_admin("daniel", "hunter2-pw")
+    server, port = _start_server()
+    try:
+        with urllib.request.urlopen(_request(port, "/login")) as r:
+            html = r.read().decode()
+            assert r.status == 200
+            assert "Furtka login" in html
+            # No setup confirm-password field rendered in login mode.
+            assert 'id="password2"' not in html
+            assert "Repeat password" not in html
+    finally:
+        server.shutdown()
+        server.server_close()
+
+
+def test_get_login_renders_setup_form_when_no_admin(fake_dirs):
+    server, port = _start_server()
+    try:
+        with urllib.request.urlopen(_request(port, "/login")) as r:
+            html = r.read().decode()
+            assert r.status == 200
+            assert "Set admin password" in html
+            assert "password2" in html  # setup confirm field rendered
+    finally:
+        server.shutdown()
+        server.server_close()
+
+
+def test_get_login_redirects_when_already_authed(fake_dirs, admin_session):
+    server, port = _start_server()
+    try:
+        opener = urllib.request.build_opener(_NoRedirectHandler())
+        try:
+            opener.open(_request(port, "/login", cookie=admin_session))
+            raise AssertionError("expected 302")
+        except urllib.error.HTTPError as e:
+            assert e.code == 302
+            assert e.headers["Location"] == "/apps"
+    finally:
+        server.shutdown()
+        server.server_close()
+
+
+def test_post_login_setup_creates_admin(fake_dirs):
+    server, port = _start_server()
+    try:
+        req = _request(
+            port,
+            "/login",
+            method="POST",
+            body={
+                "username": "daniel",
+                "password": "a-real-password",
+                "password2": "a-real-password",
+            },
+        )
+        with urllib.request.urlopen(req) as r:
+            assert r.status == 200
+            set_cookie = r.headers["Set-Cookie"]
+            assert auth.COOKIE_NAME in set_cookie
+            assert "HttpOnly" in set_cookie
+            assert "SameSite=Strict" in set_cookie
+        # users.json got written.
+        assert auth.load_users()["admin"]["username"] == "daniel"
+        # And the password really works.
+        assert auth.authenticate("daniel", "a-real-password") is True
+    finally:
+        server.shutdown()
+        server.server_close()
+
+
+def test_post_login_setup_rejects_password_mismatch(fake_dirs):
+    server, port = _start_server()
+    try:
+        req = _request(
+            port,
+            "/login",
+            method="POST",
+            body={"username": "x", "password": "abcdefgh", "password2": "different"},
+        )
+        try:
+            urllib.request.urlopen(req)
+            raise AssertionError("expected 400")
+        except urllib.error.HTTPError as e:
+            assert e.code == 400
+            body = json.loads(e.read())
+            assert "match" in body["error"].lower()
+        # No admin created.
+        assert auth.setup_needed() is True
+    finally:
+        server.shutdown()
+        server.server_close()
+
+
+def test_post_login_setup_rejects_short_password(fake_dirs):
+    server, port = _start_server()
+    try:
+        req = _request(
+            port,
+            "/login",
+            method="POST",
+            body={"username": "x", "password": "short", "password2": "short"},
+        )
+        try:
+            urllib.request.urlopen(req)
+            raise AssertionError("expected 400")
+        except urllib.error.HTTPError as e:
+            assert e.code == 400
+    finally:
+        server.shutdown()
+        server.server_close()
+
+
+def test_post_login_success_with_correct_credentials(fake_dirs):
+    auth.create_admin("daniel", "hunter2-pw")
+    server, port = _start_server()
+    try:
+        req = _request(
+            port,
+            "/login",
+            method="POST",
+            body={"username": "daniel", "password": "hunter2-pw"},
+        )
+        with urllib.request.urlopen(req) as r:
+            assert r.status == 200
+            set_cookie = r.headers["Set-Cookie"]
+            assert auth.COOKIE_NAME in set_cookie
+    finally:
+        server.shutdown()
+        server.server_close()
+
+
+def test_post_login_rejects_wrong_password(fake_dirs):
+    auth.create_admin("daniel", "hunter2-pw")
+    server, port = _start_server()
+    try:
+        req = _request(
+            port,
+            "/login",
+            method="POST",
+            body={"username": "daniel", "password": "nope"},
+        )
+        try:
+            urllib.request.urlopen(req)
+            raise AssertionError("expected 401")
+        except urllib.error.HTTPError as e:
+            assert e.code == 401
+    finally:
+        server.shutdown()
+        server.server_close()
+
+
+def test_post_logout_revokes_session(fake_dirs, admin_session):
+    server, port = _start_server()
+    try:
+        # Logout returns 200 and clears the cookie.
+        with urllib.request.urlopen(
+            _request(port, "/logout", cookie=admin_session, method="POST", body={})
+        ) as r:
+            assert r.status == 200
+            set_cookie = r.headers["Set-Cookie"]
+            assert "Max-Age=0" in set_cookie
+        # Subsequent API call with same cookie → 401 (session revoked).
+        try:
+            urllib.request.urlopen(_request(port, "/api/apps", cookie=admin_session))
+            raise AssertionError("expected 401")
+        except urllib.error.HTTPError as e:
+            assert e.code == 401
+    finally:
+        server.shutdown()
+        server.server_close()
+
+
+def test_post_to_protected_route_without_auth_is_401(fake_dirs):
+    server, port = _start_server()
+    try:
+        req = _request(
+            port,
+            "/api/apps/install",
+            method="POST",
+            body={"name": "whatever"},
+        )
+        try:
+            urllib.request.urlopen(req)
+            raise AssertionError("expected 401")
+        except urllib.error.HTTPError as e:
+            assert e.code == 401
+    finally:
+        server.shutdown()
+        server.server_close()
+
+
 # --- Settings endpoints ------------------------------------------------------
 
 SETTINGS_MANIFEST = dict(
@@ -329,7 +601,7 @@ def test_update_settings_unknown_app(fake_dirs):
     assert status == 404
 
 
-def test_http_get_settings_route(fake_dirs, no_docker):
+def test_http_get_settings_route(fake_dirs, no_docker, admin_session):
     _, bundled = fake_dirs
     _write_bundled(bundled, "fileshare", manifest=SETTINGS_MANIFEST)
     server = api.HTTPServer(("127.0.0.1", 0), api._Handler)
@@ -337,7 +609,9 @@ def test_http_get_settings_route(fake_dirs, no_docker):
     t = threading.Thread(target=server.serve_forever, daemon=True)
     t.start()
     try:
-        with urllib.request.urlopen(f"http://127.0.0.1:{port}/api/apps/fileshare/settings") as r:
+        with urllib.request.urlopen(
+            _request(port, "/api/apps/fileshare/settings", cookie=admin_session)
+        ) as r:
             assert r.status == 200
             data = json.loads(r.read())
             assert data["name"] == "fileshare"
@@ -549,7 +823,7 @@ def test_furtka_update_status_endpoint(stub_furtka_updater):
     assert stub_furtka_updater["status_called"] == 1
 
 
-def test_http_post_update_route(fake_dirs, no_docker, update_docker_stubs):
+def test_http_post_update_route(fake_dirs, no_docker, update_docker_stubs, admin_session):
     _, bundled = fake_dirs
     _write_bundled(bundled, "fileshare", env_example="A=real")
     api._do_install("fileshare")
@@ -560,11 +834,12 @@ def test_http_post_update_route(fake_dirs, no_docker, update_docker_stubs):
     t = threading.Thread(target=server.serve_forever, daemon=True)
     t.start()
     try:
-        req = urllib.request.Request(
-            f"http://127.0.0.1:{port}/api/apps/fileshare/update",
-            data=b"{}",
-            headers={"Content-Type": "application/json"},
+        req = _request(
+            port,
+            "/api/apps/fileshare/update",
+            cookie=admin_session,
             method="POST",
+            body={},
         )
         with urllib.request.urlopen(req) as r:
             assert r.status == 200
@@ -576,7 +851,7 @@ def test_http_post_update_route(fake_dirs, no_docker, update_docker_stubs):
         server.server_close()
 
 
-def test_http_post_install_with_settings(fake_dirs, no_docker):
+def test_http_post_install_with_settings(fake_dirs, no_docker, admin_session):
     _, bundled = fake_dirs
     _write_bundled(bundled, "fileshare", manifest=SETTINGS_MANIFEST)
     server = api.HTTPServer(("127.0.0.1", 0), api._Handler)
@@ -584,16 +859,15 @@ def test_http_post_install_with_settings(fake_dirs, no_docker):
     t = threading.Thread(target=server.serve_forever, daemon=True)
     t.start()
     try:
-        req = urllib.request.Request(
-            f"http://127.0.0.1:{port}/api/apps/install",
-            data=json.dumps(
-                {
+        req = _request(
+            port,
+            "/api/apps/install",
+            cookie=admin_session,
+            method="POST",
+            body={
                 "name": "fileshare",
                 "settings": {"SMB_USER": "alice", "SMB_PASSWORD": "s3cret"},
-                }
-            ).encode(),
-            headers={"Content-Type": "application/json"},
-            method="POST",
+            },
         )
         with urllib.request.urlopen(req) as r:
             assert r.status == 200

tests/test_auth.py

@@ -0,0 +1,152 @@
+import json
+from datetime import UTC, datetime, timedelta
+
+import pytest
+
+from furtka import auth
+
+
+@pytest.fixture
+def tmp_users_file(tmp_path, monkeypatch):
+    path = tmp_path / "users.json"
+    monkeypatch.setenv("FURTKA_USERS_FILE", str(path))
+    # Sessions are module-level; wipe between tests so one doesn't leak a
+    # valid token into the next.
+    auth.SESSIONS.clear()
+    return path
+
+
+def test_hash_password_roundtrip():
+    h = auth.hash_password("hunter2")
+    assert h != "hunter2"  # Not plain text.
+    assert auth.verify_password("hunter2", h) is True
+    assert auth.verify_password("hunter3", h) is False
+
+
+def test_hash_password_is_salted():
+    # Two calls with the same password must produce different hashes.
+    a = auth.hash_password("same")
+    b = auth.hash_password("same")
+    assert a != b
+    # But both verify against the original.
+    assert auth.verify_password("same", a)
+    assert auth.verify_password("same", b)
+
+
+def test_load_users_returns_empty_when_missing(tmp_users_file):
+    assert not tmp_users_file.exists()
+    assert auth.load_users() == {}
+
+
+def test_load_users_returns_empty_on_junk(tmp_users_file):
+    tmp_users_file.write_text("{not json")
+    assert auth.load_users() == {}
+
+
+def test_load_users_returns_empty_on_non_dict(tmp_users_file):
+    tmp_users_file.write_text("[]")
+    assert auth.load_users() == {}
+
+
+def test_save_users_atomic_and_0600(tmp_users_file):
+    auth.save_users({"admin": {"hash": "x", "username": "daniel"}})
+    assert tmp_users_file.exists()
+    mode = tmp_users_file.stat().st_mode & 0o777
+    assert mode == 0o600, f"expected 0o600, got {oct(mode)}"
+    loaded = json.loads(tmp_users_file.read_text())
+    assert loaded["admin"]["username"] == "daniel"
+
+
+def test_setup_needed_true_on_missing_file(tmp_users_file):
+    assert auth.setup_needed() is True
+
+
+def test_setup_needed_true_on_empty_dict(tmp_users_file):
+    tmp_users_file.write_text("{}")
+    assert auth.setup_needed() is True
+
+
+def test_setup_needed_false_when_admin_exists(tmp_users_file):
+    auth.create_admin("daniel", "secret-pw")
+    assert auth.setup_needed() is False
+
+
+def test_create_admin_overwrites_file(tmp_users_file):
+    auth.create_admin("daniel", "secret-pw")
+    auth.create_admin("robert", "new-pw")
+    users = auth.load_users()
+    assert users["admin"]["username"] == "robert"
+
+
+def test_authenticate_happy(tmp_users_file):
+    auth.create_admin("daniel", "secret-pw")
+    assert auth.authenticate("daniel", "secret-pw") is True
+
+
+def test_authenticate_wrong_username(tmp_users_file):
+    auth.create_admin("daniel", "secret-pw")
+    assert auth.authenticate("robert", "secret-pw") is False
+
+
+def test_authenticate_wrong_password(tmp_users_file):
+    auth.create_admin("daniel", "secret-pw")
+    assert auth.authenticate("daniel", "wrong") is False
+
+
+def test_authenticate_no_admin(tmp_users_file):
+    assert auth.authenticate("daniel", "anything") is False
+
+
+# ---- Session store ---------------------------------------------------------
+
+
+def test_session_create_and_lookup(tmp_users_file):
+    s = auth.SESSIONS.create("daniel")
+    assert s.username == "daniel"
+    assert s.token
+    looked_up = auth.SESSIONS.lookup(s.token)
+    assert looked_up is not None
+    assert looked_up.username == "daniel"
+
+
+def test_session_lookup_unknown_token(tmp_users_file):
+    assert auth.SESSIONS.lookup("not-a-real-token") is None
+
+
+def test_session_lookup_none_token(tmp_users_file):
+    assert auth.SESSIONS.lookup(None) is None
+    assert auth.SESSIONS.lookup("") is None
+
+
+def test_session_revoke(tmp_users_file):
+    s = auth.SESSIONS.create("daniel")
+    auth.SESSIONS.revoke(s.token)
+    assert auth.SESSIONS.lookup(s.token) is None
+
+
+def test_session_expires(tmp_users_file, monkeypatch):
+    # Build a session store with a 0-second TTL so lookup immediately
+    # treats new sessions as expired.
+    store = auth.SessionStore(ttl_seconds=0)
+    s = store.create("daniel")
+    # Force the clock forward a hair so the > check fires.
+    monkeypatch.setattr(
+        auth,
+        "datetime",
+        _FakeDatetime(datetime.now(UTC) + timedelta(seconds=1)),
+    )
+    # The module-local datetime reference inside SessionStore.lookup
+    # resolves at call time. Verify that an expired session is dropped.
+    assert store.lookup(s.token) is None
+
+
+class _FakeDatetime:
+    """Tiny shim — only `.now(tz)` is used from SessionStore."""
+
+    def __init__(self, fixed_utc):
+        self._fixed = fixed_utc
+
+    def now(self, tz=None):
+        if tz is None:
+            return self._fixed.replace(tzinfo=None)
+        return self._fixed.astimezone(tz)

tests/test_webinstaller_assets.py

@@ -54,7 +54,7 @@ def install_cmds(tmp_path, monkeypatch):
     fake = tmp_path / "payload.tar.gz"
     fake.write_bytes(b"not a real tarball")
     monkeypatch.setattr(app, "RESOURCE_MANAGER_PAYLOAD", fake)
-    return app._post_install_commands("testhost")
+    return app._post_install_commands("testhost", "daniel", "test-admin-pw")
 
 
 @pytest.mark.parametrize("target,asset_relpath", ASSET_TARGETS)
@@ -202,3 +202,28 @@ def test_read_asset_raises_for_missing_file():
 
 def test_assets_dir_resolves_to_repo_tree():
     assert app._ASSETS_DIR == ASSETS
+
+
+def test_post_install_writes_users_json_with_hashed_password(install_cmds):
+    """The Furtka-admin users.json is created during the chroot post-install.
+
+    Without this, a fresh-install box lands at /login in first-run setup
+    mode and the user has to go through the browser to set a password —
+    which defeats the "step-1 password works for everything" design. Also
+    check that the file is chmod 0600 (the PBKDF2 hash is a secret even
+    if it's slow to crack).
+    """
+    import json as _json
+
+    from werkzeug.security import check_password_hash
+
+    users_cmd = next((c for c in install_cmds if " > /var/lib/furtka/users.json" in c), None)
+    assert users_cmd is not None, "no command writes /var/lib/furtka/users.json"
+    assert "chmod 600" in users_cmd, "users.json must be chmod 0600"
+    body = _extract_written_content(users_cmd, "/var/lib/furtka/users.json")
+    parsed = _json.loads(body)
+    assert "admin" in parsed
+    assert parsed["admin"]["username"] == "daniel"  # matches fixture
+    # Hash is a real werkzeug hash, not the plaintext password.
+    assert parsed["admin"]["hash"] != "test-admin-pw"
+    assert check_password_hash(parsed["admin"]["hash"], "test-admin-pw")

webinstaller/app.py

@@ -8,6 +8,7 @@ import os
 import re
 import subprocess
 import sys
+from datetime import UTC
 from pathlib import Path
 
 from drives import list_scored_devices
@@ -348,7 +349,35 @@ def _furtka_json_cmd(hostname):
     )
 
 
-def _post_install_commands(hostname):
+def _users_json_cmd(username, password):
+    """Write /var/lib/furtka/users.json with the admin account hashed.
+
+    The core furtka-api reads this file on every login attempt; the
+    auth.py module treats `admin.username` + `admin.hash` as the only
+    credential. Hashing happens here in the webinstaller (werkzeug is a
+    flask transitive dep so it's already installed in this environment)
+    — the chroot doesn't need pip. Mode 0600 so nobody but root on the
+    installed box can read the PBKDF2 hash.
+    """
+    from datetime import datetime
+
+    from werkzeug.security import generate_password_hash
+
+    users = {
+        "admin": {
+            "username": username,
+            "hash": generate_password_hash(password),
+            "created_at": datetime.now(UTC).isoformat(timespec="seconds"),
+        }
+    }
+    return _write_file_cmd(
+        "/var/lib/furtka/users.json",
+        json.dumps(users, indent=2) + "\n",
+        mode="600",
+    )
+
+
+def _post_install_commands(hostname, admin_username, admin_password):
     # nss-mdns: splice `mdns_minimal [NOTFOUND=return]` before `resolve` on
     # the hosts line so `*.local` works from the installed system too. Guarded
     # so a re-run (or a future Arch default that already ships mdns) is a
@@ -389,6 +418,12 @@ def _post_install_commands(hostname):
         # furtka.json depends on /opt/furtka/current/VERSION, so it has to
         # run after the resource-manager commands.
         _furtka_json_cmd(hostname),
+        # Admin account for the Furtka web UI. Hashed here (werkzeug is
+        # already in scope for the Flask webinstaller) and materialised
+        # into /var/lib/furtka/users.json at mode 0600 on the target
+        # partition — the installed core's auth.py picks it up on first
+        # login.
+        _users_json_cmd(admin_username, admin_password),
     ]
 
 
@@ -447,7 +482,7 @@ def build_archinstall_config(s):
         # page, status timer, and welcome banner into place.
         "custom_commands": [
             f"gpasswd -a {s['username']} docker",
-            *_post_install_commands(s["hostname"]),
+            *_post_install_commands(s["hostname"], s["username"], s["password"]),
         ],
         "network_config": {"type": "iso"},
         "ssh": True,