* the service must recognize <code>ETag</code>, <code>Last-Modified</code> and <code>Cache-Control: none</code> provided by the client and act accordingly.
* every answer to a GET request must include proper <code>Cache-Control</code> headers
* every PUT and PATCH request to update an object must include the <code>ETag</code> provided by the <code>GET</code> request to fetch the object initially. The API must respond with an <code>428 (Precondition Required)</code> if the ETag is missing.
''Implementation notes'':