title: S3.getSignedUrl to accept multiple content-type
body: <p>I'm using the <code>react-s3-uploader</code> node package, which takes in a <code>signingUrl</code>for obtaining a signedUrl for storing an object into S3.</p>
  
  <p>Currently I've configured a lambda function (with an API Gateway endpoint) to generate this signedUrl. After some tinkering, I've got it to work, but noticed that I have to define in my lambda function the <code>content-type</code>, which looks like this:</p>
  
  <pre><code>var AWS = require('aws-sdk');
  const S3 = new AWS.S3()
  AWS.config.update({
    region: 'us-west-2'
  })
  
  exports.handler = function(event, context) {
    console.log('context, ', context)
    console.log('event, ', event)
    var params = {
      Bucket: 'video-bucket',
      Key: 'videoname.mp4',
      Expires: 120,
      ACL: 'public-read',
      ContentType:'video/mp4'
    };
    S3.getSignedUrl('putObject', params, function (err, url) {
      console.log('The URL is', url);
      context.done(null, {signedUrl: url})
    });  
  }
  </code></pre>
  
  <p>The issue is that I want this signed url to be able to accept multiple types of video files, and I've tried setting <code>ContentType</code> to <code>video/*</code>, which doesn't work. Also, because this lambda endpoint isn't what actually takes the upload, I can't pass in the filetype to this function beforehand.</p>