Issues with setting headers

should be:

curl_setopt($ch, CURLOPT_HTTPHEADER, array(
    'Accept: application/vnd.twitchtv.v3+json',
    'Authorization: OAuth ' .$_SESSION['user']['token']
));

The call to CURLOPT_HEADER controls if the HTTP HEADERS are passed back from the Request to curl_exec (as further more directed by CURLOPT_RETURNTRANSFER)

Please see the documentation