if (isset($_SERVER['HTTPS']))
    $scheme = $_SERVER['HTTPS'];
else
    $scheme = '';
if (($scheme) && ($scheme != 'off')) $scheme = 'https';
else $scheme = 'http';

/*

if ((isset($_SERVER['REQUEST_SCHEME']) AND $_SERVER['REQUEST_SCHEME'] === 'https') OR (isset($_SERVER['HTTPS']) AND $_SERVER['HTTPS'] === 'on'))
    $protocol = 'https';
else
    $protocol = 'http';
    
*/