Adds a HTTP header to the POST request.
$au.imageUploaderFlash('uploaderID').metadata().uploadRequestHeaders(keyValuePairs);
Type: Object
Key-value pairs specifying the header name and content, e.g.{'X-My-Custom-Header1': 'My value', 'X-My-Custom-Header2': 'Another value'}
To add multiple headers, specify several key-value pairs. If you call this method multiple times, old values are removed and replaced by the new one. For example, if you want to clear custom headers, just pass an empty object {}.
Calling this method without an argument will return a current header object. It is useful if you need to append a new header to the existing ones.