feat(auth): gate OSS signup behind ENABLE_SIGNUP flag (#514)

* feat(auth): gate OSS signup behind ENABLE_SIGNUP flag

## Problem

The `POST /api/v1/auth/signup` endpoint is unconditionally exposed on
every OSS install. Operators running an invite-only deployment (private
customer instances, staging environments, internal-only tenants) have
no way to disable public account creation without patching the codebase.
The UI also shows the "Sign up" link on `/auth/login` regardless of
whether signup is available, so a locked-down deployment leaves broken
navigation on the login page.

## Fix

Introduce a single `ENABLE_SIGNUP` env var (default `true` — no behavior
change for existing installs) that controls signup end-to-end:

- **Backend** — `api/constants.ENABLE_SIGNUP` is read at module load.
  The signup handler returns 403 when it's false. Also exposed on
  `GET /api/v1/health` as `signup_enabled: bool` so the UI can mirror
  the operator's choice at runtime instead of at bundle-build time.

- **UI** — `getSignupEnabled()` in `lib/auth/config.ts` proxies the
  health field, `/api/config/auth` surfaces it to the browser, the
  login page conditionally renders the "Sign up" link via a one-shot
  `fetch("/api/config/auth")` in `useEffect`, and the middleware
  redirects `/auth/signup` → `/auth/login` when disabled (fires before
  Next.js can serve the statically-prerendered signup page).

- **Helm** — `config.enableSignup` (default `true`) is rendered into
  the ConfigMap as `ENABLE_SIGNUP` so operators can flip it via
  `--set config.enableSignup=false` at install/upgrade time.

Fallbacks default to `signupEnabled: true` in every layer so a fresh
install "just works" and matches the backend default.

* address review: rollout on ConfigMap change, cache TTL, no signup-link flash

Four review points on #514:

**P1 — ConfigMap Change Skips Rollout** (`configmap.yaml`). `helm upgrade
--set config.enableSignup=false` updated the ConfigMap but did NOT roll
the api pods, so running processes kept the ENABLE_SIGNUP env from
startup and continued serving the old signup behavior — including
divergence between replicas mid-upgrade.

Fix: add the standard `checksum/config` pod-template annotation on the
four backend Deployments that `envFrom` the ConfigMap (`web`,
`arq-worker`, `ari-manager`, `campaign-orchestrator`). Verified with
`helm template`: all four Deployments share the same checksum on any
given render, and flipping `config.enableSignup` changes the checksum
uniformly so kubectl sees a pod-template diff and rolls all four.

**P1 — Signup Flag Stays Cached (server)** (`ui/src/lib/auth/config.ts`).
Module-scoped cache had no TTL. `revalidate: 300` was passed on the
underlying `fetch()` but the in-memory short-circuit above ran first, so
the value never refreshed until the UI pod restarted.

Fix: add `AUTH_CONFIG_TTL_MS = 5 * 60 * 1000` (matching the fetch
revalidate hint) so the module cache and the Next fetch cache stay in
sync. Backend flag flips propagate within 5 minutes without a pod
restart.

**P1 — Middleware Redirect Uses Stale State** (`ui/src/middleware.ts`).
Same shape as above — a separate module cache with no expiry could keep
redirecting `/auth/signup → /auth/login` after signup was re-enabled, or
keep serving the statically-prerendered signup page after lockdown.

Fix: same `SERVER_CONFIG_TTL_MS = 5 * 60 * 1000` TTL on the middleware
cache.

**P2 — Signup link flash on login page** (`ui/src/app/auth/login/page.tsx`).
Initial `signupEnabled` state was `null`, so `{signupEnabled && ...}`
hid the link on first paint and it popped in after the fetch resolved
— a CLS on every login-page load on stock installs where signup is
enabled.

Fix: initialise the state to `true` (matches the backend default). The
fetch still overrides to `false` when the operator has actually
disabled signup, so the lockdown UI behavior is unchanged; only the
happy-path flash is gone.

* simplify signup flag: drop TTL caches and middleware redirect

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

* resolve signup flag server-side to avoid signup link flicker

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

---------

Co-authored-by: prabhat pankaj <prabhatiitbhu@gmail.com>
Co-authored-by: Abhishek Kumar <abhishek@a6k.me>
Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

ui/src/app/api/config/auth/route.ts

@@ -1,6 +1,6 @@
 import { NextResponse } from 'next/server';
 
-import { getAuthProvider, getStackConfig } from '@/lib/auth/config';
+import { getAuthProvider, getSignupEnabled, getStackConfig } from '@/lib/auth/config';
 import logger from '@/lib/logger';
 
 export async function GET() {
@@ -8,10 +8,12 @@ export async function GET() {
   // When using Stack, hand the public client config to the browser so it can
   // initialize the Stack SDK at runtime (no build-time NEXT_PUBLIC_* needed).
   const stackConfig = provider === 'stack' ? await getStackConfig() : null;
+  const signupEnabled = await getSignupEnabled();
   logger.debug(`Got provider ${provider} from getAuthProvider`)
   return NextResponse.json({
     provider,
     stackProjectId: stackConfig?.projectId ?? null,
     stackPublishableClientKey: stackConfig?.publishableClientKey ?? null,
+    signupEnabled,
   });
 }

ui/src/app/auth/login/LoginForm.tsx

@@ -0,0 +1,96 @@
+"use client";
+
+import Link from "next/link";
+import { useState } from "react";
+import { toast } from "sonner";
+
+import { loginApiV1AuthLoginPost } from "@/client/sdk.gen";
+import { AuthEnterpriseCTA } from "@/components/auth/AuthEnterpriseCTA";
+import { AuthShell } from "@/components/auth/AuthShell";
+import { Button } from "@/components/ui/button";
+import { Input } from "@/components/ui/input";
+import { Label } from "@/components/ui/label";
+
+export function LoginForm({ signupEnabled }: { signupEnabled: boolean }) {
+  const [email, setEmail] = useState("");
+  const [password, setPassword] = useState("");
+  const [loading, setLoading] = useState(false);
+
+  const handleSubmit = async (e: React.FormEvent) => {
+    e.preventDefault();
+    setLoading(true);
+
+    try {
+      const res = await loginApiV1AuthLoginPost({
+        body: { email, password },
+      });
+
+      if (res.error || !res.data) {
+        const detail = (res.error as { detail?: string })?.detail;
+        toast.error(detail || "Login failed");
+        return;
+      }
+
+      // Set httpOnly cookies via server route
+      await fetch("/api/auth/session", {
+        method: "POST",
+        headers: { "Content-Type": "application/json" },
+        body: JSON.stringify({ token: res.data.token, user: res.data.user }),
+      });
+
+      window.location.href = "/after-sign-in";
+    } catch {
+      toast.error("An error occurred. Please try again.");
+    } finally {
+      setLoading(false);
+    }
+  };
+
+  return (
+    <AuthShell enterpriseSlot={<AuthEnterpriseCTA />}>
+      <div className="space-y-1.5 text-center">
+        <h1 className="text-2xl font-semibold tracking-tight">Sign in</h1>
+        <p className="text-sm text-muted-foreground">
+          Enter your email and password to continue
+        </p>
+      </div>
+
+      <form onSubmit={handleSubmit} className="space-y-4">
+        <div className="space-y-2">
+          <Label htmlFor="email">Email</Label>
+          <Input
+            id="email"
+            type="email"
+            placeholder="you@example.com"
+            value={email}
+            onChange={(e) => setEmail(e.target.value)}
+            required
+          />
+        </div>
+        <div className="space-y-2">
+          <Label htmlFor="password">Password</Label>
+          <Input
+            id="password"
+            type="password"
+            placeholder="Enter your password"
+            value={password}
+            onChange={(e) => setPassword(e.target.value)}
+            required
+          />
+        </div>
+        <Button type="submit" className="w-full" disabled={loading}>
+          {loading ? "Signing in..." : "Sign in"}
+        </Button>
+      </form>
+
+      {signupEnabled && (
+        <p className="text-center text-sm text-muted-foreground">
+          Don&apos;t have an account?{" "}
+          <Link href="/auth/signup" className="text-primary underline-offset-4 hover:underline">
+            Sign up
+          </Link>
+        </p>
+      )}
+    </AuthShell>
+  );
+}

ui/src/app/auth/login/page.tsx

@@ -1,94 +1,14 @@
-"use client";
+import { getSignupEnabled } from "@/lib/auth/config";
 
-import Link from "next/link";
-import { useState } from "react";
-import { toast } from "sonner";
+import { LoginForm } from "./LoginForm";
 
-import { loginApiV1AuthLoginPost } from "@/client/sdk.gen";
-import { AuthEnterpriseCTA } from "@/components/auth/AuthEnterpriseCTA";
-import { AuthShell } from "@/components/auth/AuthShell";
-import { Button } from "@/components/ui/button";
-import { Input } from "@/components/ui/input";
-import { Label } from "@/components/ui/label";
+// Resolve the backend health check before rendering so the "Sign up" link is
+// correct on first paint — no client-side fetch, no flicker on locked-down
+// installs. force-dynamic keeps the page off the build-time prerender, which
+// would bake in the flag's build-environment value.
+export const dynamic = "force-dynamic";
 
-export default function LoginPage() {
-  const [email, setEmail] = useState("");
-  const [password, setPassword] = useState("");
-  const [loading, setLoading] = useState(false);
-
-  const handleSubmit = async (e: React.FormEvent) => {
-    e.preventDefault();
-    setLoading(true);
-
-    try {
-      const res = await loginApiV1AuthLoginPost({
-        body: { email, password },
-      });
-
-      if (res.error || !res.data) {
-        const detail = (res.error as { detail?: string })?.detail;
-        toast.error(detail || "Login failed");
-        return;
-      }
-
-      // Set httpOnly cookies via server route
-      await fetch("/api/auth/session", {
-        method: "POST",
-        headers: { "Content-Type": "application/json" },
-        body: JSON.stringify({ token: res.data.token, user: res.data.user }),
-      });
-
-      window.location.href = "/after-sign-in";
-    } catch {
-      toast.error("An error occurred. Please try again.");
-    } finally {
-      setLoading(false);
-    }
-  };
-
-  return (
-    <AuthShell enterpriseSlot={<AuthEnterpriseCTA />}>
-      <div className="space-y-1.5 text-center">
-        <h1 className="text-2xl font-semibold tracking-tight">Sign in</h1>
-        <p className="text-sm text-muted-foreground">
-          Enter your email and password to continue
-        </p>
-      </div>
-
-      <form onSubmit={handleSubmit} className="space-y-4">
-        <div className="space-y-2">
-          <Label htmlFor="email">Email</Label>
-          <Input
-            id="email"
-            type="email"
-            placeholder="you@example.com"
-            value={email}
-            onChange={(e) => setEmail(e.target.value)}
-            required
-          />
-        </div>
-        <div className="space-y-2">
-          <Label htmlFor="password">Password</Label>
-          <Input
-            id="password"
-            type="password"
-            placeholder="Enter your password"
-            value={password}
-            onChange={(e) => setPassword(e.target.value)}
-            required
-          />
-        </div>
-        <Button type="submit" className="w-full" disabled={loading}>
-          {loading ? "Signing in..." : "Sign in"}
-        </Button>
-      </form>
-
-      <p className="text-center text-sm text-muted-foreground">
-        Don&apos;t have an account?{" "}
-        <Link href="/auth/signup" className="text-primary underline-offset-4 hover:underline">
-          Sign up
-        </Link>
-      </p>
-    </AuthShell>
-  );
+export default async function LoginPage() {
+  const signupEnabled = await getSignupEnabled();
+  return <LoginForm signupEnabled={signupEnabled} />;
 }

ui/src/client/types.gen.ts

@@ -2884,6 +2884,10 @@ export type HealthResponse = {
      * Force Turn Relay
      */
     force_turn_relay: boolean;
+    /**
+     * Signup Enabled
+     */
+    signup_enabled: boolean;
     /**
      * Stack Project Id
      */

ui/src/lib/auth/config.ts

@@ -10,6 +10,7 @@ export interface StackConfig {
 interface ResolvedAuthConfig {
   authProvider: string;
   stackConfig: StackConfig | null;
+  signupEnabled: boolean;
 }
 
 let cachedConfig: ResolvedAuthConfig | null = null;
@@ -45,7 +46,10 @@ async function resolveAuthConfig(): Promise<ResolvedAuthConfig> {
                 data.stack_publishable_client_key as string,
             }
           : null;
-      cachedConfig = { authProvider, stackConfig };
+      // Default to signup-enabled when the backend omits the field (older api
+      // versions before the flag existed) — matches the backend's own default.
+      const signupEnabled = data.signup_enabled !== false;
+      cachedConfig = { authProvider, stackConfig, signupEnabled };
       return cachedConfig;
     }
   } catch {
@@ -56,7 +60,7 @@ async function resolveAuthConfig(): Promise<ResolvedAuthConfig> {
   // do NOT cache it: caching here would pin the entire UI to local auth until a
   // container restart if the first resolution loses the startup race with the api
   // service. Leaving it uncached means the next request retries and self-heals.
-  return { authProvider: "local", stackConfig: null };
+  return { authProvider: "local", stackConfig: null, signupEnabled: true };
 }
 
 /**
@@ -73,3 +77,11 @@ export async function getAuthProvider(): Promise<string> {
 export async function getStackConfig(): Promise<StackConfig | null> {
   return (await resolveAuthConfig()).stackConfig;
 }
+
+/**
+ * Returns true when the backend allows signup (`ENABLE_SIGNUP`, default true).
+ * The login page uses this to hide the signup link on locked-down installs.
+ */
+export async function getSignupEnabled(): Promise<boolean> {
+  return (await resolveAuthConfig()).signupEnabled;
+}