How do I create a signature using the imageUploadtoS3 option in Froala with Coldfusion 8?

Question

I want to use Froala text editor to upload images directly to my Amazon S3 account. An S3 authentication signature is required.

ImageUploadtoS3 javascript:

$('.selector').editable({
  imageUploadToS3: {
    bucket: 'editor',
    region: 's3',
    keyStart: 'uploads/',
    callback: function (url, key) {
      // The URL and Key returned from Amazon.
      console.log (url);
      console.log (key);
    },
    params: {
      acl: 'public-read', // ACL according to Amazon Documentation.
      AWSAccessKeyId: 'ACCESS_KEY', // Access Key from Amazon.
      policy: 'POLICY_STRING', // Policy string computed in the backend.
      signature: '', // Signature computed in the backend.
    }
  }
});

How do I generate that signature? I'm using Coldfusion 8. Thanks for your help.