diff --git a/src/__tests__/pages/auth/signin.test.jsx b/src/__tests__/pages/auth/signin.test.jsx
index c9babf09d..261a327d2 100644
--- a/src/__tests__/pages/auth/signin.test.jsx
+++ b/src/__tests__/pages/auth/signin.test.jsx
@@ -3,21 +3,27 @@
 import { render, screen, waitFor } from "@testing-library/react";
 import { describe, expect, it, vi } from "vitest";
 
-const { getSettingsMock } = vi.hoisted(() => ({
+const { getSettingsMock, authOptionsMock } = vi.hoisted(() => ({
   getSettingsMock: vi.fn(),
+  authOptionsMock: vi.fn(),
 }));
 
 vi.mock("utils/config/config", () => ({
   getSettings: getSettingsMock,
 }));
 
+vi.mock("pages/api/auth/[...nextauth]", () => ({
+  get authOptions() {
+    return authOptionsMock();
+  },
+}));
+
 vi.mock("next/router", () => ({
   useRouter: () => ({
     query: {},
   }),
 }));
 
-import { getProviders } from "next-auth/react";
 import SignInPage, { getServerSideProps } from "pages/auth/signin";
 
 describe("pages/auth/signin", () => {
@@ -33,7 +39,7 @@ describe("pages/auth/signin", () => {
       />,
     );
 
-    expect(screen.getByText("Authentication not configured")).toBeInTheDocument();
+    expect(screen.getByText("Authentication error")).toBeInTheDocument();
 
     await waitFor(() => {
       expect(document.documentElement.classList.contains("dark")).toBe(true);
@@ -61,7 +67,7 @@ describe("pages/auth/signin", () => {
   });
 
   it("getServerSideProps returns providers and only public sign-in settings", async () => {
-    getProviders.mockResolvedValueOnce({ foo: { id: "foo", name: "Foo" } });
+    authOptionsMock.mockReturnValueOnce({ providers: [{ id: "foo", name: "Foo", type: "oauth" }] });
     getSettingsMock.mockReturnValueOnce({
       theme: "dark",
       color: "slate",
@@ -79,11 +85,10 @@ describe("pages/auth/signin", () => {
 
     const res = await getServerSideProps({});
 
-    expect(getProviders).toHaveBeenCalled();
     expect(getSettingsMock).toHaveBeenCalled();
     expect(res).toEqual({
       props: {
-        providers: { foo: { id: "foo", name: "Foo" } },
+        providers: { foo: { id: "foo", name: "Foo", type: "oauth" } },
         settings: {
           theme: "dark",
           color: "slate",
@@ -96,4 +101,18 @@ describe("pages/auth/signin", () => {
     expect(res.props.settings).not.toHaveProperty("providers");
     expect(res.props.settings).not.toHaveProperty("layout");
   });
+
+  it("getServerSideProps falls back to no providers when auth options fail to load", async () => {
+    const consoleError = vi.spyOn(console, "error").mockImplementation(() => {});
+    authOptionsMock.mockImplementationOnce(() => {
+      throw new Error("Homepage auth is enabled but HOMEPAGE_EXTERNAL_URL (or NEXTAUTH_URL) is missing.");
+    });
+    getSettingsMock.mockReturnValueOnce({ theme: "dark" });
+
+    const res = await getServerSideProps({});
+
+    expect(res.props.providers).toEqual({});
+    expect(consoleError).toHaveBeenCalled();
+    consoleError.mockRestore();
+  });
 });
diff --git a/src/instrumentation.js b/src/instrumentation.js
new file mode 100644
index 000000000..84b763f19
--- /dev/null
+++ b/src/instrumentation.js
@@ -0,0 +1,7 @@
+import { applyNextAuthEnv } from "utils/env";
+
+export function register() {
+  if (process.env.NEXT_RUNTIME !== "nodejs") return;
+
+  applyNextAuthEnv();
+}
diff --git a/src/instrumentation.test.js b/src/instrumentation.test.js
new file mode 100644
index 000000000..b3bc3d5da
--- /dev/null
+++ b/src/instrumentation.test.js
@@ -0,0 +1,53 @@
+import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
+
+describe("instrumentation", () => {
+  const originalEnv = process.env;
+
+  beforeEach(() => {
+    vi.resetModules();
+    process.env = { ...originalEnv };
+    delete process.env.NEXTAUTH_SECRET;
+    delete process.env.NEXTAUTH_URL;
+    delete process.env.HOMEPAGE_AUTH_SECRET;
+    delete process.env.HOMEPAGE_EXTERNAL_URL;
+    process.env.NEXT_RUNTIME = "nodejs";
+  });
+
+  afterEach(() => {
+    process.env = originalEnv;
+  });
+
+  it("maps HOMEPAGE_* auth envs to their NextAuth equivalents", async () => {
+    process.env.HOMEPAGE_AUTH_SECRET = "secret";
+    process.env.HOMEPAGE_EXTERNAL_URL = "https://homepage.example";
+    const { register } = await import("./instrumentation");
+
+    register();
+
+    expect(process.env.NEXTAUTH_SECRET).toBe("secret");
+    expect(process.env.NEXTAUTH_URL).toBe("https://homepage.example");
+  });
+
+  it("does not override explicitly configured NextAuth envs", async () => {
+    process.env.HOMEPAGE_AUTH_SECRET = "secret";
+    process.env.HOMEPAGE_EXTERNAL_URL = "https://homepage.example";
+    process.env.NEXTAUTH_SECRET = "explicit-secret";
+    process.env.NEXTAUTH_URL = "https://explicit.example";
+    const { register } = await import("./instrumentation");
+
+    register();
+
+    expect(process.env.NEXTAUTH_SECRET).toBe("explicit-secret");
+    expect(process.env.NEXTAUTH_URL).toBe("https://explicit.example");
+  });
+
+  it("is a no-op outside the node runtime", async () => {
+    process.env.NEXT_RUNTIME = "edge";
+    process.env.HOMEPAGE_EXTERNAL_URL = "https://homepage.example";
+    const { register } = await import("./instrumentation");
+
+    register();
+
+    expect(process.env.NEXTAUTH_URL).toBeUndefined();
+  });
+});
diff --git a/src/pages/api/auth/[...nextauth].js b/src/pages/api/auth/[...nextauth].js
index a133e922b..ce5a9f505 100644
--- a/src/pages/api/auth/[...nextauth].js
+++ b/src/pages/api/auth/[...nextauth].js
@@ -3,7 +3,7 @@ import { createHash, timingSafeEqual } from "node:crypto";
 import NextAuth from "next-auth";
 import CredentialsProvider from "next-auth/providers/credentials";
 
-import { isAuthEnabled } from "utils/env";
+import { applyNextAuthEnv, isAuthEnabled } from "utils/env";
 import createLogger from "utils/logger";
 
 const MIN_AUTH_SECRET_LENGTH = 32;
@@ -12,20 +12,13 @@ const authEnabled = isAuthEnabled();
 const issuer = process.env.HOMEPAGE_OIDC_ISSUER;
 const clientId = process.env.HOMEPAGE_OIDC_CLIENT_ID;
 const clientSecret = process.env.HOMEPAGE_OIDC_CLIENT_SECRET;
-const homepageAuthSecret = process.env.HOMEPAGE_AUTH_SECRET;
-const homepageExternalUrl = process.env.HOMEPAGE_EXTERNAL_URL;
 const homepageAuthPassword = process.env.HOMEPAGE_AUTH_PASSWORD;
 const homepageAuthPasswordDigest = homepageAuthPassword
   ? createHash("sha256").update(homepageAuthPassword, "utf8").digest()
   : null;
 
-// Map HOMEPAGE_* envs to what NextAuth expects
-if (!process.env.NEXTAUTH_SECRET && homepageAuthSecret) {
-  process.env.NEXTAUTH_SECRET = homepageAuthSecret;
-}
-if (!process.env.NEXTAUTH_URL && homepageExternalUrl) {
-  process.env.NEXTAUTH_URL = homepageExternalUrl;
-}
+// Also done in instrumentation.js
+applyNextAuthEnv();
 
 const defaultScope = process.env.HOMEPAGE_OIDC_SCOPE || "openid email profile";
 const cleanedIssuer = issuer ? issuer.replace(/\/+$/, "") : issuer;
diff --git a/src/pages/auth/signin.jsx b/src/pages/auth/signin.jsx
index fad910091..5f803bf53 100644
--- a/src/pages/auth/signin.jsx
+++ b/src/pages/auth/signin.jsx
@@ -1,5 +1,5 @@
 import classNames from "classnames";
-import { getProviders, signIn } from "next-auth/react";
+import { signIn } from "next-auth/react";
 import { useRouter } from "next/router";
 import { useEffect, useMemo, useState } from "react";
 import { BiShieldQuarter } from "react-icons/bi";
@@ -94,10 +94,8 @@ export default function SignIn({ providers, settings }) {
             <div className="mx-auto flex h-12 w-12 items-center justify-center rounded-2xl bg-theme-500/15 text-theme-600 dark:text-theme-300">
               <BiShieldQuarter className="h-6 w-6" />
             </div>
-            <h1 className="mt-6 text-2xl font-semibold text-gray-900 dark:text-slate-100">
-              Authentication not configured
-            </h1>
-            <p className="mt-3 text-sm text-gray-600 dark:text-slate-400">OIDC is disabled or misconfigured.</p>
+            <h1 className="mt-6 text-2xl font-semibold text-gray-900 dark:text-slate-100">Authentication error</h1>
+            <p className="mt-3 text-sm text-gray-600 dark:text-slate-400">Auth is disabled or misconfigured.</p>
           </div>
         </main>
       </>
@@ -202,7 +200,16 @@ export default function SignIn({ providers, settings }) {
 }
 
 export async function getServerSideProps(context) {
-  const providers = await getProviders();
+  // Avoid getProviders() fetch
+  let providers = {};
+  try {
+    // Dynamic so a bad config throws in here rather than at page load
+    const { authOptions } = await import("pages/api/auth/[...nextauth]");
+    providers = Object.fromEntries(authOptions.providers.map(({ id, name, type }) => [id, { id, name, type }]));
+  } catch (e) {
+    console.error("Unable to load auth providers: %s", e.message);
+  }
+
   const homepageSettings = getSettings();
   const settings = Object.fromEntries(
     PUBLIC_SIGN_IN_SETTINGS.filter((key) => Object.prototype.hasOwnProperty.call(homepageSettings, key)).map((key) => [
diff --git a/src/utils/env.js b/src/utils/env.js
index da03d2e9f..14982d433 100644
--- a/src/utils/env.js
+++ b/src/utils/env.js
@@ -1,3 +1,13 @@
 export function isAuthEnabled() {
   return process.env.HOMEPAGE_AUTH_ENABLED === "true";
 }
+
+// Frozen at module load, so map them before anything imports it
+export function applyNextAuthEnv() {
+  if (!process.env.NEXTAUTH_SECRET && process.env.HOMEPAGE_AUTH_SECRET) {
+    process.env.NEXTAUTH_SECRET = process.env.HOMEPAGE_AUTH_SECRET;
+  }
+  if (!process.env.NEXTAUTH_URL && process.env.HOMEPAGE_EXTERNAL_URL) {
+    process.env.NEXTAUTH_URL = process.env.HOMEPAGE_EXTERNAL_URL;
+  }
+}
diff --git a/vitest.setup.js b/vitest.setup.js
index 1c5328ba3..6c03bd6d7 100644
--- a/vitest.setup.js
+++ b/vitest.setup.js
@@ -11,7 +11,6 @@ afterEach(() => {
 // Avoid NextAuth client-side fetches during unit tests.
 vi.mock("next-auth/react", () => ({
   SessionProvider: ({ children }) => children ?? null,
-  getProviders: vi.fn(async () => ({})),
 }));
 
 // implement a couple of common formatters mocked in next-i18next