This method accepts an array of configuration options:
- url: (string) URL of the resource being signed (can include query
string and wildcards). For example: http://d111111abcdef8.cloudfront.net/images/horizon.jpg?size=large&license=yes
- policy: (string) JSON policy. Use this option when creating a signed
URL for a custom policy.
- expires: (int) UTC Unix timestamp used when signing with a canned
policy. Not required when passing a custom 'policy' option.
- key_pair_id: (string) The ID of the key pair used to sign CloudFront
URLs for private distributions.
- private_key: (string) The filepath ot the private key used to sign
CloudFront URLs for private distributions.