fix(asset-proxy): be sure all headers are passed to the final endpoint

__tests__/asset-proxy.ts

@@ -47,11 +47,18 @@ test('request to https://asset-proxy.serlo.org/image?url=* gets asset from url q
 
 test('request to asset-proxy works also in case of other encodings', async () => {
   const env = currentTestEnvironment()
-  const response = await env.fetch({
-    subdomain: 'asset-proxy',
-    pathname:
-      '/image?url=https://upload.wikimedia.org/wikipedia/commons/8/8b/Sinus_mit_y.svg',
-  })
+  const response = await env.fetch(
+    {
+      subdomain: 'asset-proxy',
+      pathname:
+        '/image?url=https://upload.wikimedia.org/wikipedia/commons/8/8b/Sinus_mit_y.svg',
+    },
+    {
+      headers: {
+        'Accept-Encoding': '*',
+      },
+    },
+  )
   expect(response.status).toBe(200)
   expect(response.headers.get('content-type')).toBe('image/svg+xml')
   expect(response.headers.get('Set-Cookie')).toBeNull()

src/asset-proxy.ts

@@ -18,10 +18,12 @@ export async function assetProxy(request: Request): Promise<Response | null> {
     return getPlaceholder()
   }
 
-  const originalResponse = await fetch(assetUrl, {
-    cf: { cacheTtl: 24 * 60 * 60 * 30 },
-    headers: { 'Accept-Encoding': '*' },
-  })
+  const originalResponse = await fetch(
+    new Request(assetUrl.toString(), request),
+    {
+      cf: { cacheTtl: 24 * 60 * 60 * 30 },
+    },
+  )
 
   if (originalResponse.ok && isImageResponse(originalResponse)) {
     const response = new Response(originalResponse.body, originalResponse)