fix(proxy): keep admin login and assets working on plain-HTTP hosts

The /admin guard always read the `__Secure-` session cookie, but Auth.js
only uses that name when AUTH_URL (or the request) is HTTPS. With an
http:// AUTH_URL a signed-in admin was bounced between /admin and /login
until the browser threw "too many history calls". The guard now picks the
cookie name the same way Auth.js does.

The CSP also sent `upgrade-insecure-requests` to plain-HTTP visitors, so
the browser rewrote same-origin fonts/scripts to https:// where nothing
listens. It is now only sent when the visitor reached us over HTTPS.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

src/lib/csp.test.ts

@@ -35,4 +35,12 @@ describe("csp", () => {
 		expect(csp).not.toContain("upgrade-insecure-requests");
 		vi.unstubAllEnvs();
 	});
+
+	it("omits upgrade-insecure-requests for plain-HTTP visitors in production", () => {
+		vi.stubEnv("NODE_ENV", "production");
+		const csp = buildContentSecurityPolicy("n", { secure: false });
+		expect(csp).toContain("frame-ancestors 'none'");
+		expect(csp).not.toContain("upgrade-insecure-requests");
+		vi.unstubAllEnvs();
+	});
 });

src/lib/csp.ts

@@ -2,8 +2,13 @@
  * Build a Content-Security-Policy value.
  * Scripts/styles: per-request nonce for Next.js and ThemeVars inline tags.
  * style-src-attr keeps 'unsafe-inline' so React `style={{…}}` attributes work.
+ * `secure` reports whether the visitor reached us over HTTPS; it gates
+ * `upgrade-insecure-requests`.
  */
-export function buildContentSecurityPolicy(nonce: string): string {
+export function buildContentSecurityPolicy(
+	nonce: string,
+	{ secure = true }: { secure?: boolean } = {},
+): string {
 	const isDev = process.env.NODE_ENV === "development";
 	const scriptSrc = [
 		"'self'",
@@ -30,15 +35,16 @@ export function buildContentSecurityPolicy(nonce: string): string {
 		"frame-src 'self' https://challenges.cloudflare.com https://www.google.com/recaptcha/",
 		// Clickjacking defence that also covers the `frame-ancestors`-aware
 		// browsers X-Frame-Options cannot reach. `upgrade-insecure-requests` is
-		// production-only: over plain-HTTP localhost it would rewrite same-origin
+		// only sent to HTTPS visitors outside development: over plain HTTP
-		// asset URLs to https and break the dev server.
+		// (localhost, a LAN/WSL IP without TLS) it rewrites same-origin asset
+		// URLs to https, where nothing listens, and fonts/scripts fail to load.
 		"frame-ancestors 'none'",
 		"connect-src 'self' https: wss:",
 		"font-src 'self' data: https://fonts.gstatic.com",
 		"object-src 'none'",
 		"base-uri 'self'",
 		"form-action 'self'",
-		...(isDev ? [] : ["upgrade-insecure-requests"]),
+		...(isDev || !secure ? [] : ["upgrade-insecure-requests"]),
 	].join("; ");
 }
 

src/lib/proxy-access.test.ts

@@ -1,7 +1,9 @@
 // @ts-nocheck
 import { describe, expect, it } from "vitest";
 import {
+	authUsesSecureCookies,
 	isCacheableAssetPath,
+	isHttpsRequest,
 	shouldRedirectAdminRequest,
 } from "./proxy-access";
 
@@ -37,3 +39,32 @@ describe("isCacheableAssetPath", () => {
 		expect(isCacheableAssetPath("/admin/media")).toBe(false);
 	});
 });
+
+describe("isHttpsRequest", () => {
+	it("trusts the first forwarded proto over the internal hop", () => {
+		expect(isHttpsRequest("https", "http:")).toBe(true);
+		expect(isHttpsRequest("https, http", "http:")).toBe(true);
+		expect(isHttpsRequest("http", "http:")).toBe(false);
+	});
+
+	it("falls back to the URL Next saw", () => {
+		expect(isHttpsRequest(null, "https:")).toBe(true);
+		expect(isHttpsRequest(null, "http:")).toBe(false);
+	});
+});
+
+describe("authUsesSecureCookies", () => {
+	it("follows AUTH_URL when it is set, like Auth.js", () => {
+		expect(authUsesSecureCookies("http://172.23.71.35", "https", "http:")).toBe(
+			false,
+		);
+		expect(
+			authUsesSecureCookies("https://hotel.example", "http", "http:"),
+		).toBe(true);
+	});
+
+	it("uses the request scheme without AUTH_URL", () => {
+		expect(authUsesSecureCookies(undefined, "https", "http:")).toBe(true);
+		expect(authUsesSecureCookies(undefined, null, "http:")).toBe(false);
+	});
+});

src/lib/proxy-access.ts

@@ -11,6 +11,37 @@ export function shouldRedirectAdminRequest(
 	return token === null;
 }
 
+/**
+ * Whether the visitor reached us over HTTPS. Behind Traefik/nginx Next only
+ * sees plain HTTP, so the first `X-Forwarded-Proto` value wins.
+ */
+export function isHttpsRequest(
+	forwardedProto: string | null,
+	requestProtocol: string,
+): boolean {
+	const proto = forwardedProto?.split(",")[0]?.trim() || requestProtocol;
+	return proto.replace(/:$/, "").toLowerCase() === "https";
+}
+
+/**
+ * Mirrors how Auth.js picks the session cookie name (`__Secure-` prefix or
+ * not): AUTH_URL decides when set, otherwise the request scheme does.
+ */
+export function authUsesSecureCookies(
+	authUrl: string | undefined,
+	forwardedProto: string | null,
+	requestProtocol: string,
+): boolean {
+	if (authUrl) {
+		try {
+			return new URL(authUrl).protocol === "https:";
+		} catch {
+			// Auth.js would reject a malformed AUTH_URL too; fall through.
+		}
+	}
+	return isHttpsRequest(forwardedProto, requestProtocol);
+}
+
 const CACHEABLE_ASSET_PREFIXES = ["/api/imaging/", "/api/media/"];
 
 export function isCacheableAssetPath(pathname: string): boolean {

src/proxy.ts

@@ -5,8 +5,10 @@ import { buildContentSecurityPolicy, createCspNonce } from "@/lib/csp";
 import { isSuspiciousPath } from "@/lib/ddos";
 import { ddosReject, enforceDdosRateLimit } from "@/lib/ddos-guard";
 import {
+	authUsesSecureCookies,
 	isCacheableAssetPath,
 	isEdgeCacheablePublicPath,
+	isHttpsRequest,
 	shouldRedirectAdminRequest,
 } from "@/lib/proxy-access";
 
@@ -43,11 +45,19 @@ export const proxy = async (req: import("next/server").NextRequest) => {
 	// Only /admin needs a real session token for the redirect guard; skipping
 	// JWT decoding on every other request keeps the proxy cheap under load.
 	const adminPath = pathname === "/admin" || pathname.startsWith("/admin/");
+	const forwardedProto = req.headers.get("x-forwarded-proto");
 	const token = adminPath
 		? await getToken({
 				req,
 				secret: env.AUTH_SECRET,
-				secureCookie: true,
+				// Must match the cookie name Auth.js chose at sign-in, otherwise a
+				// signed-in admin on a plain-HTTP AUTH_URL is bounced between
+				// /admin and /login forever.
+				secureCookie: authUsesSecureCookies(
+					process.env.AUTH_URL ?? process.env.NEXTAUTH_URL,
+					forwardedProto,
+					req.nextUrl.protocol,
+				),
 			})
 		: null;
 
@@ -60,7 +70,9 @@ export const proxy = async (req: import("next/server").NextRequest) => {
 	}
 
 	const nonce = createCspNonce();
-	const csp = buildContentSecurityPolicy(nonce);
+	const csp = buildContentSecurityPolicy(nonce, {
+		secure: isHttpsRequest(forwardedProto, req.nextUrl.protocol),
+	});
 
 	const headers = new Headers(req.headers);
 	headers.set("x-pathname", pathname);