diff --git a/.env.example b/.env.example
index 5e6fab3..121dff4 100644
--- a/.env.example
+++ b/.env.example
@@ -6,6 +6,12 @@ DATABASE_URL=postgresql://lyra:lyra@db:5432/lyra
 # 32 random bytes, base64. Generate with: openssl rand -base64 32
 LYRA_SECRET_KEY=MDEyMzQ1Njc4OWFiY2RlZjAxMjM0NTY3ODlhYmNkZWY=
 
+# Shared password protecting the whole web UI + API. When set, every request must sign in
+# (one shared password, no per-user accounts). LEAVE UNSET AND THE APP IS OPEN to anyone
+# who can reach the host — only safe on a trusted LAN or behind a VPN/auth proxy. Strongly
+# recommended for any exposed deployment. See README "Security".
+# LYRA_PASSWORD=change-me
+
 # Host directory for the downloaded music library (bind-mounted into the worker at /music)
 MUSIC_DIR=./music
 
diff --git a/README.md b/README.md
index e785ae3..ea98ea1 100644
--- a/README.md
+++ b/README.md
@@ -124,3 +124,20 @@ docker compose start web worker
 `--clean --if-exists` drops and recreates each object, so restoring over an existing DB
 is safe. To restore onto a brand-new host, bring up just `db` first
 (`docker compose up -d db`), restore, then `up -d --build` the rest.
+
+## Security
+
+Lyra has **no per-user accounts**. Two layers protect it:
+
+- **Shared-password gate.** Set `LYRA_PASSWORD` in `.env` to require a single shared
+  password for the entire UI and API. A request without a valid session cookie is
+  redirected to `/login` (or gets `401` for `/api/*`). The cookie is httpOnly and carries
+  an HMAC of the password keyed by `LYRA_SECRET_KEY`, so it can't be forged. **If
+  `LYRA_PASSWORD` is unset, the app is completely open** — anyone who can reach the host
+  can browse the library, trigger downloads, and read/overwrite the stored credentials in
+  Settings. Set it for any deployment that isn't on a fully trusted, isolated network.
+
+- **Network.** The shared password is deliberately minimal (single password, bearer
+  cookie, plain HTTP on the LAN). For anything internet-facing, also put Lyra behind a
+  reverse proxy with TLS and/or a VPN or auth gateway — don't rely on the shared password
+  alone.
diff --git a/docker-compose.yml b/docker-compose.yml
index afe68db..8d415aa 100644
--- a/docker-compose.yml
+++ b/docker-compose.yml
@@ -22,6 +22,8 @@ services:
     environment:
       DATABASE_URL: ${DATABASE_URL}
       LYRA_SECRET_KEY: ${LYRA_SECRET_KEY}
+      # Optional shared-password gate for the whole UI/API. Unset ⇒ app is open. See README.
+      LYRA_PASSWORD: ${LYRA_PASSWORD:-}
     ports:
       # host:container — host 8770 avoids the Quill app on 3000 (and Lidarr on 8686)
       - "8770:3000"
diff --git a/web/src/app/_ui/contents-nav.tsx b/web/src/app/_ui/contents-nav.tsx
index a6c88b3..3c31c38 100644
--- a/web/src/app/_ui/contents-nav.tsx
+++ b/web/src/app/_ui/contents-nav.tsx
@@ -13,6 +13,7 @@ const LINKS: { href: string; label: string }[] = [
 
 export function ContentsNav() {
   const pathname = usePathname();
+  if (pathname === "/login") return null; // no section nav on the login screen
   const active = (href: string) => (href === "/" ? pathname === "/" : pathname.startsWith(href));
   return (
     <nav className="contents">
diff --git a/web/src/app/_ui/masthead.tsx b/web/src/app/_ui/masthead.tsx
index 1456840..66e7700 100644
--- a/web/src/app/_ui/masthead.tsx
+++ b/web/src/app/_ui/masthead.tsx
@@ -1,7 +1,9 @@
 import { ThemeToggle } from "./theme-toggle";
 import { WorkerStatus } from "./worker-status";
+import { SignOut } from "./sign-out";
 
 export function Masthead() {
+  const authEnabled = !!process.env.LYRA_PASSWORD;
   return (
     <header className="masthead">
       <div className="wordmark">
@@ -13,6 +15,7 @@ export function Masthead() {
       <div className="press-status">
         <WorkerStatus />
         <ThemeToggle />
+        {authEnabled ? <SignOut /> : null}
       </div>
     </header>
   );
diff --git a/web/src/app/_ui/sign-out.tsx b/web/src/app/_ui/sign-out.tsx
new file mode 100644
index 0000000..a910780
--- /dev/null
+++ b/web/src/app/_ui/sign-out.tsx
@@ -0,0 +1,20 @@
+"use client";
+
+import { usePathname } from "next/navigation";
+
+/** Clears the auth cookie and returns to /login. Rendered only when auth is enabled. */
+export function SignOut() {
+  const pathname = usePathname();
+  if (pathname === "/login") return null;
+
+  async function signOut() {
+    await fetch("/api/auth", { method: "DELETE" }).catch(() => {});
+    window.location.assign("/login");
+  }
+
+  return (
+    <button type="button" className="sign-out" onClick={signOut} aria-label="sign out">
+      Sign out
+    </button>
+  );
+}
diff --git a/web/src/app/_ui/worker-status.tsx b/web/src/app/_ui/worker-status.tsx
index b30ad6a..5096151 100644
--- a/web/src/app/_ui/worker-status.tsx
+++ b/web/src/app/_ui/worker-status.tsx
@@ -1,12 +1,16 @@
 "use client";
 
 import { useEffect, useState } from "react";
+import { usePathname } from "next/navigation";
 
 /** Live worker liveness in the masthead — polls /api/worker (heartbeat recency). */
 export function WorkerStatus() {
   const [online, setOnline] = useState<boolean | null>(null);
+  const pathname = usePathname();
+  const onLogin = pathname === "/login";
 
   useEffect(() => {
+    if (onLogin) return; // don't poll (would 401) on the login screen
     let alive = true;
     async function check() {
       try {
@@ -22,8 +26,9 @@ export function WorkerStatus() {
       alive = false;
       clearInterval(id);
     };
-  }, []);
+  }, [onLogin]);
 
+  if (onLogin) return null;
   const label = online === null ? "…" : online ? "listening" : "offline";
   return (
     <div className={`worker-status${online === false ? " off" : ""}`}>
diff --git a/web/src/app/api/auth/route.ts b/web/src/app/api/auth/route.ts
new file mode 100644
index 0000000..b6fd6aa
--- /dev/null
+++ b/web/src/app/api/auth/route.ts
@@ -0,0 +1,44 @@
+import { NextResponse } from "next/server";
+import { AUTH_COOKIE, expectedToken } from "@/lib/auth";
+
+// POST /api/auth — exchange the shared password for a session cookie.
+// DELETE /api/auth — log out (clear the cookie).
+export async function POST(request: Request) {
+  const token = await expectedToken();
+  if (!token) {
+    // No password configured — auth is disabled, nothing to log in to.
+    return NextResponse.json({ ok: true, authDisabled: true });
+  }
+
+  let password = "";
+  const ctype = request.headers.get("content-type") ?? "";
+  if (ctype.includes("application/json")) {
+    const body = (await request.json().catch(() => ({}))) as { password?: unknown };
+    password = typeof body.password === "string" ? body.password : "";
+  } else {
+    const form = await request.formData().catch(() => null);
+    password = form ? String(form.get("password") ?? "") : "";
+  }
+
+  if (password !== process.env.LYRA_PASSWORD) {
+    return NextResponse.json({ ok: false, error: "Incorrect password" }, { status: 401 });
+  }
+
+  const res = NextResponse.json({ ok: true });
+  res.cookies.set(AUTH_COOKIE, token, {
+    httpOnly: true,
+    sameSite: "lax",
+    path: "/",
+    // NOT `secure`: Lyra serves plain HTTP on the LAN (:8770); a Secure cookie would be
+    // dropped by the browser and cause a login redirect loop. Works fine behind an HTTPS
+    // proxy too (Secure is not required, only recommended).
+    maxAge: 60 * 60 * 24 * 30, // 30 days
+  });
+  return res;
+}
+
+export async function DELETE() {
+  const res = NextResponse.json({ ok: true });
+  res.cookies.set(AUTH_COOKIE, "", { httpOnly: true, path: "/", maxAge: 0 });
+  return res;
+}
diff --git a/web/src/app/design.css b/web/src/app/design.css
index 4b59677..d919eb3 100644
--- a/web/src/app/design.css
+++ b/web/src/app/design.css
@@ -172,6 +172,29 @@ nav.contents .sep { flex: 1; }
   .job .chip { grid-column: 2 / 3; justify-self: start; margin-top: 12px; }
 }
 
+/* ── Login ────────────────────────────────────────────── */
+.login { display: flex; justify-content: center; padding: 48px 0; }
+.login-panel {
+  border: 1.5px solid var(--rule-2); padding: 34px 32px; max-width: 380px; width: 100%;
+}
+.login-panel .eyebrow {
+  font-family: var(--mono); font-size: 0.64rem; letter-spacing: 0.16em; text-transform: uppercase;
+  color: var(--accent); margin: 0 0 8px;
+}
+.login-panel h1 { font-family: var(--serif); font-size: 1.9rem; margin: 0 0 6px; }
+.login-lede { color: var(--graphite); margin: 0 0 22px; font-size: 0.9rem; }
+.login-form { display: flex; flex-direction: column; gap: 18px; align-items: stretch; }
+.login-form .field input { min-width: 0; }
+.login-form .btn { align-self: flex-start; }
+.login-error {
+  font-family: var(--mono); font-size: 0.72rem; letter-spacing: 0.04em; color: var(--accent); margin: 0;
+}
+.sign-out {
+  font-family: var(--mono); font-size: 0.64rem; letter-spacing: 0.14em; text-transform: uppercase;
+  color: var(--graphite); background: transparent; border: 0; cursor: pointer; padding: 0;
+}
+.sign-out:hover { color: var(--accent); }
+
 /* ── Phase 2: page headers, list rows, tools ──────────── */
 .page-head { margin: 6px 0 26px; }
 .page-head .eyebrow {
diff --git a/web/src/app/login/login-form.tsx b/web/src/app/login/login-form.tsx
new file mode 100644
index 0000000..7f12e1b
--- /dev/null
+++ b/web/src/app/login/login-form.tsx
@@ -0,0 +1,56 @@
+"use client";
+
+import { useState } from "react";
+import { useRouter, useSearchParams } from "next/navigation";
+
+export function LoginForm() {
+  const router = useRouter();
+  const params = useSearchParams();
+  const next = params.get("next") || "/";
+  const [password, setPassword] = useState("");
+  const [error, setError] = useState("");
+  const [busy, setBusy] = useState(false);
+
+  async function submit(e: React.FormEvent) {
+    e.preventDefault();
+    setBusy(true);
+    setError("");
+    try {
+      const res = await fetch("/api/auth", {
+        method: "POST",
+        headers: { "content-type": "application/json" },
+        body: JSON.stringify({ password }),
+      });
+      if (res.ok) {
+        // full navigation so middleware re-evaluates with the new cookie
+        window.location.assign(next);
+        return;
+      }
+      const data = (await res.json().catch(() => ({}))) as { error?: string };
+      setError(data.error || "Login failed");
+      setBusy(false);
+    } catch {
+      setError("Login failed");
+      setBusy(false);
+    }
+  }
+
+  return (
+    <form className="login-form" onSubmit={submit}>
+      <label className="field">
+        <span>Password</span>
+        <input
+          type="password"
+          autoFocus
+          value={password}
+          onChange={(e) => setPassword(e.target.value)}
+          placeholder="shared password"
+        />
+      </label>
+      {error ? <p className="login-error">{error}</p> : null}
+      <button className="btn accent" type="submit" disabled={busy || !password}>
+        {busy ? "Entering…" : "Enter"}
+      </button>
+    </form>
+  );
+}
diff --git a/web/src/app/login/page.tsx b/web/src/app/login/page.tsx
new file mode 100644
index 0000000..7a519e9
--- /dev/null
+++ b/web/src/app/login/page.tsx
@@ -0,0 +1,19 @@
+import { Suspense } from "react";
+import { LoginForm } from "./login-form";
+
+export const metadata = { title: "Sign in · Lyra" };
+
+export default function LoginPage() {
+  return (
+    <main className="login">
+      <div className="login-panel">
+        <p className="eyebrow">Restricted pressing</p>
+        <h1>Sign in</h1>
+        <p className="login-lede">This Lyra instance is password-protected.</p>
+        <Suspense>
+          <LoginForm />
+        </Suspense>
+      </div>
+    </main>
+  );
+}
diff --git a/web/src/lib/auth.test.ts b/web/src/lib/auth.test.ts
new file mode 100644
index 0000000..501e4d0
--- /dev/null
+++ b/web/src/lib/auth.test.ts
@@ -0,0 +1,40 @@
+import { describe, it, expect, beforeEach } from "vitest";
+import { expectedToken, safeEqual } from "./auth";
+
+beforeEach(() => {
+  process.env.LYRA_SECRET_KEY = "MDEyMzQ1Njc4OWFiY2RlZjAxMjM0NTY3ODlhYmNkZWY=";
+  delete process.env.LYRA_PASSWORD;
+});
+
+describe("auth token", () => {
+  it("returns '' when no password is configured (auth disabled)", async () => {
+    expect(await expectedToken()).toBe("");
+  });
+
+  it("derives a stable, non-empty token from the password", async () => {
+    process.env.LYRA_PASSWORD = "hunter2";
+    const a = await expectedToken();
+    const b = await expectedToken();
+    expect(a).not.toBe("");
+    expect(a).toBe(b); // deterministic
+  });
+
+  it("changes with the password and with the secret key", async () => {
+    process.env.LYRA_PASSWORD = "hunter2";
+    const base = await expectedToken();
+    process.env.LYRA_PASSWORD = "different";
+    expect(await expectedToken()).not.toBe(base);
+    process.env.LYRA_PASSWORD = "hunter2";
+    process.env.LYRA_SECRET_KEY = "ZmZmZmZmZmZmZmZmZmZmZmZmZmZmZmZmZmZmZmZmZmY=";
+    expect(await expectedToken()).not.toBe(base);
+  });
+});
+
+describe("safeEqual", () => {
+  it("matches equal strings and rejects others", () => {
+    expect(safeEqual("abc", "abc")).toBe(true);
+    expect(safeEqual("abc", "abd")).toBe(false);
+    expect(safeEqual("abc", "ab")).toBe(false);
+    expect(safeEqual("", "")).toBe(true);
+  });
+});
diff --git a/web/src/lib/auth.ts b/web/src/lib/auth.ts
new file mode 100644
index 0000000..d43e733
--- /dev/null
+++ b/web/src/lib/auth.ts
@@ -0,0 +1,39 @@
+// Minimal shared-password auth. Enabled ONLY when LYRA_PASSWORD is set; otherwise the
+// app stays open (unchanged behavior) — see README "Security". The auth cookie holds a
+// token derived from the password via HMAC-SHA256 keyed by LYRA_SECRET_KEY, so it can't
+// be forged without the secret and the plaintext password is never stored client-side.
+// Edge-safe: uses global Web Crypto + btoa (no node:crypto / Buffer), so the same code
+// runs in middleware (Edge runtime) and in the API route (Node runtime).
+
+export const AUTH_COOKIE = "lyra_auth";
+
+function toB64(bytes: Uint8Array): string {
+  let s = "";
+  for (const b of bytes) s += String.fromCharCode(b);
+  return btoa(s);
+}
+
+/** The token a valid session cookie must carry, or "" when auth is disabled (no password). */
+export async function expectedToken(): Promise<string> {
+  const password = process.env.LYRA_PASSWORD;
+  if (!password) return "";
+  const secret = process.env.LYRA_SECRET_KEY ?? "lyra";
+  const enc = new TextEncoder();
+  const key = await crypto.subtle.importKey(
+    "raw",
+    enc.encode(secret),
+    { name: "HMAC", hash: "SHA-256" },
+    false,
+    ["sign"],
+  );
+  const sig = await crypto.subtle.sign("HMAC", key, enc.encode(password));
+  return toB64(new Uint8Array(sig));
+}
+
+/** Constant-time string compare (both operands are our own derived tokens). */
+export function safeEqual(a: string, b: string): boolean {
+  if (a.length !== b.length) return false;
+  let diff = 0;
+  for (let i = 0; i < a.length; i++) diff |= a.charCodeAt(i) ^ b.charCodeAt(i);
+  return diff === 0;
+}
diff --git a/web/src/middleware.ts b/web/src/middleware.ts
new file mode 100644
index 0000000..742251f
--- /dev/null
+++ b/web/src/middleware.ts
@@ -0,0 +1,28 @@
+import { NextResponse, type NextRequest } from "next/server";
+import { AUTH_COOKIE, expectedToken, safeEqual } from "@/lib/auth";
+
+// Gate every request behind the shared password when LYRA_PASSWORD is set. The /login
+// page and the auth API are always reachable; static assets are excluded via `matcher`.
+export async function middleware(req: NextRequest) {
+  const token = await expectedToken();
+  if (!token) return NextResponse.next(); // auth disabled (no LYRA_PASSWORD)
+
+  const { pathname } = req.nextUrl;
+  if (pathname === "/login" || pathname === "/api/auth") return NextResponse.next();
+
+  const cookie = req.cookies.get(AUTH_COOKIE)?.value ?? "";
+  if (safeEqual(cookie, token)) return NextResponse.next();
+
+  if (pathname.startsWith("/api/")) {
+    return new NextResponse("Unauthorized", { status: 401 });
+  }
+  const url = req.nextUrl.clone();
+  url.pathname = "/login";
+  url.searchParams.set("next", pathname + req.nextUrl.search);
+  return NextResponse.redirect(url);
+}
+
+export const config = {
+  // Run on everything except Next internals and static assets (which carry no secrets).
+  matcher: ["/((?!_next/static|_next/image|favicon.ico|icon.svg|fonts/).*)"],
+};