I had success with this example:
<?
$service_url = 'https://restapi.e-conomic.com/employees';
$curl = curl_init($service_url);
//$curl_post_data = array(
curl_setopt($curl, CURLOPT_HTTPHEADER, array(
'X-AppSecretToken:MySecretToken',
'X-AgreementGrantToken:MyGrantToken',
'Content-Type:application/json'
));
curl_setopt($curl, CURLOPT_RETURNTRANSFER, true);
curl_setopt($curl, CURLOPT_GET, true);
//curl_setopt($curl, CURLOPT_POSTFIELDS, $curl_post_data);
$curl_response = curl_exec($curl);
curl_close($curl);
$json = json_decode($curl_response);
print "<pre>";
print_r($json);
print "</pre>";
?>