uat→main (PROD): GRO-2586 CORS origin allowlist enforcement (frozen @2d4edb6) (#221)

uat→main (PROD): GRO-2586 CORS origin allowlist enforcement (frozen @2d4edb6)

src/lib/auth-cors.ts

@@ -0,0 +1,22 @@
+/**
+ * Enforces the trusted-origins CORS allowlist on a raw Response from Better Auth.
+ * Better Auth reflects the request Origin into Access-Control-Allow-Origin
+ * regardless of the trustedOrigins config, allowing credentialed cross-origin reads
+ * from arbitrary attacker origins. This wrapper strips CORS headers for any origin
+ * not in the allowlist. (GRO-2586)
+ */
+export function enforceAuthCors(
+  requestOrigin: string | undefined,
+  trustedOrigins: string[],
+  res: Response
+): Response {
+  const headers = new Headers(res.headers);
+  if (requestOrigin && trustedOrigins.includes(requestOrigin)) {
+    headers.set("Access-Control-Allow-Origin", requestOrigin);
+    headers.set("Access-Control-Allow-Credentials", "true");
+  } else {
+    headers.delete("Access-Control-Allow-Origin");
+    headers.delete("Access-Control-Allow-Credentials");
+  }
+  return new Response(res.body, { status: res.status, statusText: res.statusText, headers });
+}