src/System/Input.php
public static function getScheme()
    {
        $protocol = isset($_SERVER['REQUEST_SCHEME']) ? strtolower($_SERVER['REQUEST_SCHEME']) : 'http';
        if ($protocol == 'http' && self::isSsl()) {
            $protocol .= 's';
        }
        return $protocol;
    }
public static function getScheme()
    {
        $protocol = isset($_SERVER['REQUEST_SCHEME']) ? strtolower($_SERVER['REQUEST_SCHEME']) : 'http';
        if ($protocol == 'http' && self::isSsl()) {
            $protocol .= 's';
        }
        return $protocol;
    }
Get scheme.

@return string