preserve auth headers in json proxies

frontend/app/api/auth/referral/apply/route.ts

@@ -2,6 +2,7 @@ import { NextRequest, NextResponse } from "next/server";
 import {
   applyAuthResponseCookies,
   buildBackendRequestHeaders,
+  buildJsonBackendRequestHeaders,
 } from "@/lib/backend-auth";
 import {
   buildProxyExceptionResponse,
@@ -22,10 +23,7 @@ export async function POST(req: NextRequest) {
     const body = await req.text();
     const res = await fetch(`${API_BASE}/api/auth/referral/apply`, {
       method: "POST",
-      headers: {
-        ...auth.headers,
-        "Content-Type": "application/json",
-      },
+      headers: buildJsonBackendRequestHeaders(auth.headers),
       body,
       cache: "no-store",
     });

frontend/app/api/ops/config/route.ts

@@ -1,5 +1,5 @@
 import { NextRequest, NextResponse } from "next/server";
-import { applyAuthResponseCookies, buildBackendRequestHeaders } from "@/lib/backend-auth";
+import { applyAuthResponseCookies, buildBackendRequestHeaders, buildJsonBackendRequestHeaders } from "@/lib/backend-auth";
 import { buildProxyExceptionResponse } from "@/lib/api-proxy";
 import { requireOpsProxyAuth } from "@/lib/ops-proxy-auth";
 
@@ -28,7 +28,7 @@ export async function PUT(req: NextRequest) {
     if (authError) return authError;
 
     const body = await req.text();
-    const res = await fetch(BACKEND, { method: "PUT", headers: { ...auth.headers, "Content-Type": "application/json" }, body, cache: "no-store" });
+    const res = await fetch(BACKEND, { method: "PUT", headers: buildJsonBackendRequestHeaders(auth.headers), body, cache: "no-store" });
     const raw = await res.text();
     const response = new NextResponse(raw, { status: res.status, headers: { "Content-Type": "application/json", "Cache-Control": "no-store" } });
     return applyAuthResponseCookies(response, auth.response);

frontend/app/api/ops/sensitive-config/route.ts

@@ -1,5 +1,5 @@
 import { NextRequest, NextResponse } from "next/server";
-import { applyAuthResponseCookies, buildBackendRequestHeaders } from "@/lib/backend-auth";
+import { applyAuthResponseCookies, buildBackendRequestHeaders, buildJsonBackendRequestHeaders } from "@/lib/backend-auth";
 import { buildProxyExceptionResponse } from "@/lib/api-proxy";
 import { requireOpsProxyAuth } from "@/lib/ops-proxy-auth";
 
@@ -28,7 +28,7 @@ export async function PUT(req: NextRequest) {
     if (authError) return authError;
 
     const body = await req.text();
-    const res = await fetch(BACKEND, { method: "PUT", headers: { ...auth.headers, "Content-Type": "application/json" }, body, cache: "no-store" });
+    const res = await fetch(BACKEND, { method: "PUT", headers: buildJsonBackendRequestHeaders(auth.headers), body, cache: "no-store" });
     const raw = await res.text();
     const response = new NextResponse(raw, { status: res.status, headers: { "Content-Type": "application/json", "Cache-Control": "no-store" } });
     return applyAuthResponseCookies(response, auth.response);

frontend/app/api/ops/subscriptions/extend/route.ts

@@ -1,5 +1,5 @@
 import { NextRequest, NextResponse } from "next/server";
-import { applyAuthResponseCookies, buildBackendRequestHeaders } from "@/lib/backend-auth";
+import { applyAuthResponseCookies, buildBackendRequestHeaders, buildJsonBackendRequestHeaders } from "@/lib/backend-auth";
 import { buildProxyExceptionResponse } from "@/lib/api-proxy";
 import { requireOpsProxyAuth } from "@/lib/ops-proxy-auth";
 
@@ -14,9 +14,9 @@ export async function POST(req: NextRequest) {
     if (authError) return authError;
 
     const body = await req.text();
-    const headers: Record<string, string> = { ...auth.headers as Record<string, string>, "Content-Type": "application/json" };
+    const headers = buildJsonBackendRequestHeaders(auth.headers);
     if (ENTITLEMENT_TOKEN) {
-      headers.Authorization = `Bearer ${ENTITLEMENT_TOKEN}`;
+      headers.set("Authorization", `Bearer ${ENTITLEMENT_TOKEN}`);
     }
     const res = await fetch(`${API_BASE}/api/ops/subscriptions/extend`, {
       method: "POST", headers, body, cache: "no-store",

frontend/app/api/ops/subscriptions/grant/route.ts

@@ -2,6 +2,7 @@ import { NextRequest, NextResponse } from "next/server";
 import {
   applyAuthResponseCookies,
   buildBackendRequestHeaders,
+  buildJsonBackendRequestHeaders,
 } from "@/lib/backend-auth";
 import { buildProxyExceptionResponse } from "@/lib/api-proxy";
 import { requireOpsProxyAuth } from "@/lib/ops-proxy-auth";
@@ -166,7 +167,7 @@ export async function POST(req: NextRequest) {
 
     const res = await fetch(`${API_BASE}/api/ops/subscriptions/grant`, {
       method: "POST",
-      headers: { ...(auth.headers as Record<string, string>), "Content-Type": "application/json" },
+      headers: buildJsonBackendRequestHeaders(auth.headers),
       body,
       cache: "no-store",
     });

frontend/app/api/ops/users/grant-points/route.ts

@@ -2,6 +2,7 @@ import { NextRequest, NextResponse } from "next/server";
 import {
   applyAuthResponseCookies,
   buildBackendRequestHeaders,
+  buildJsonBackendRequestHeaders,
 } from "@/lib/backend-auth";
 import { buildProxyExceptionResponse } from "@/lib/api-proxy";
 import { requireOpsProxyAuth } from "@/lib/ops-proxy-auth";
@@ -24,10 +25,7 @@ export async function POST(req: NextRequest) {
     const body = await req.text();
     const res = await fetch(`${API_BASE}/api/ops/users/grant-points`, {
       method: "POST",
-      headers: {
-        ...auth.headers,
-        "Content-Type": "application/json",
-      },
+      headers: buildJsonBackendRequestHeaders(auth.headers),
       body,
       cache: "no-store",
     });

frontend/components/ops/__tests__/backendAuthHeaders.test.ts

@@ -0,0 +1,40 @@
+import fs from "node:fs";
+import path from "node:path";
+
+function assert(condition: unknown, message: string): asserts condition {
+  if (!condition) throw new Error(message);
+}
+
+function collectRouteFiles(dir: string): string[] {
+  return fs.readdirSync(dir, { withFileTypes: true }).flatMap((entry) => {
+    const fullPath = path.join(dir, entry.name);
+    if (entry.isDirectory()) return collectRouteFiles(fullPath);
+    return entry.name === "route.ts" ? [fullPath] : [];
+  });
+}
+
+export function runTests() {
+  const projectRoot = process.cwd();
+  const apiRoot = path.join(projectRoot, "app", "api");
+  const unsafeRoutes = collectRouteFiles(apiRoot)
+    .filter((routePath) =>
+      /\.\.\.\s*(?:\(\s*)?auth\.headers/.test(fs.readFileSync(routePath, "utf8")),
+    )
+    .map((routePath) => path.relative(projectRoot, routePath));
+
+  assert(
+    unsafeRoutes.length === 0,
+    `backend auth Headers must not be object-spread because that drops authorization headers: ${unsafeRoutes.join(", ")}`,
+  );
+
+  const helperSource = fs.readFileSync(
+    path.join(projectRoot, "lib", "backend-auth.ts"),
+    "utf8",
+  );
+  assert(
+    helperSource.includes("buildJsonBackendRequestHeaders") &&
+      helperSource.includes("new Headers(headers)") &&
+      helperSource.includes('result.set("Content-Type", "application/json")'),
+    "backend auth must expose a safe JSON header builder",
+  );
+}

frontend/lib/backend-auth.ts

@@ -125,6 +125,12 @@ export function applyAuthResponseCookies(
   return target;
 }
 
+export function buildJsonBackendRequestHeaders(headers: HeadersInit) {
+  const result = new Headers(headers);
+  result.set("Content-Type", "application/json");
+  return result;
+}
+
 export function requireBackendAuthUser(auth: BackendHeaderBuildResult) {
   if (auth.authUserId) return null;
   return applyAuthResponseCookies(