add X-Requested-With header to fetch() requests

CHANGELOG.md

@@ -5,6 +5,8 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 ## Unreleased
+### Fixed
+- Make Cadenza return an error instead of showing an error page.
 
 ## 2.10.0 - 2024-06-11
 ### Added

src/cadenza.js

@@ -851,7 +851,13 @@ export class CadenzaClient {
   ) {
     const url = this.#createUrl(path, params);
     this.#log('Fetch', url.toString());
-    const res = await fetch(url, { signal });
+    const res = await fetch(url, {
+      signal,
+      headers: {
+        // Make Cadenza return an error instead of showing an error page.
+        'X-Requested-With': 'XMLHttpRequest'
+      }
+    });
     if (!res.ok) {
       const errorType =
         {