title: Getting S3 to always include a Vary header in its response
body: <p>I have CORS headers set up on S3, and when a browser makes a CORS request (i.e. includes an <code>Origin</code> header), S3 adds all the right headers to the response, including a <code>Vary</code> header. However, if the request does not include an <code>Origin</code> header, the response does not include a <code>Vary</code> header, which leaves intermediate caches (such as CDNs) free to cache the response and serve it when a later request comes in, even if that later request adds an <code>Origin</code> header. </p>
  
  <p>How can I get S3 to always return a <code>Vary</code> header?</p>