/*y.php ye göndermek istediğin veriler form elemanları yani*/
$data = array(
/* örnek  name=username value="admin */
    'username' => 'admin',
    'password' => 'admin'
);
 
$payload = json_encode($data);
 
$ch = curl_init('https://example.com/y.php');
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLINFO_HEADER_OUT, true);
curl_setopt($ch, CURLOPT_POST, true);
curl_setopt($ch, CURLOPT_POSTFIELDS, $payload);
$result = curl_exec($ch);
curl_close($ch);
/*y.php den gelen veriler*/
print_r($result);