When I browse to a page with Firefox and click a download link, the following headers are shown when I inspect the request in network inspector:
Connection: keep-
Example:
Accept
text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Encoding
gzip, deflate
Accept-Language
nl,en-US;q=0.7,en;q=0.3
Connection
keep-alive
Cookie
_ga=GA1.2.598213448.1471644637; _gat=1
Host
mariannesdelights.be
User-Agent
Mozilla/5.0 (Windows NT 10.0; WOW64; rv:47.0) Gecko/20100101 Firefox/47.0
$headers = array('HeaderName:HeaderValue','HeaderName2:HeaderValue2');
curl_setopt($ch,CURLOPT_HTTPHEADER,$headers);
That should produce the exact same HTTP-Response headers.