Add extra headers required for CORS

Add the following HTTP headers required for CORS:

 - Access-Control-Max-Age
 - Access-Control-Allow-Credentials
 - Access-Control-Allow-Methods
 - Access-Control-Allow-Headers
 - Origin

Definitions taken from the [Mozilla documentation].

[Mozilla documentation]: https://developer.mozilla.org/en-US/docs/HTTP/Access_control_CORS