title: AWS S3 pre signed URL without Expiry date
body: <p>Is there any way that I can generate Pre-Signed URL's without any expiry date ?
  I'm developing a Email app where my attachments will be saved in S3.
  Also please let me know what is the best way to download attachments via JavaScript SDK. </p>
  
  <p>I'm using below code </p>
  
  <pre><code>var params = {Bucket: 'bucket', Key: 'key', Expires: 60};
  var url = s3.getSignedUrl('getObject', params);
  console.log('The URL is', url);
  </code></pre>