is_https.php

<?php

function is_https() {
    // dont use `filter_input(INPUT_SERVER, '...')`:
    // https://github.com/xwp/stream/issues/254
    $https = isset($_SERVER['HTTPS']) ? $_SERVER['HTTPS'] : '';
    if (!empty($https)) {
        $https = strtolower($https);
        if ($https == 'on') {
            return true;
        }
    }
    
    $proto = isset($_SERVER['HTTP_X_FORWARDED_PROTO']) ? $_SERVER['HTTP_X_FORWARDED_PROTO'] : '';
    if (!empty($proto)) {
        $proto = strtolower($proto);
        if ($proto == 'https') {
            return true;
        }
    }

    $port = isset($_SERVER['SERVER_PORT']) ? $_SERVER['SERVER_PORT'] : '';
    if ($port == 443) {
        return true;
    }

    $front_end_https = isset($_SERVER['HTTP_FRONT_END_HTTPS']) ? $_SERVER['HTTP_FRONT_END_HTTPS'] : '';
    if (!empty($front_end_https)) {
        $front_end_https = strtolower($front_end_https);
        if ($front_end_https == 'on') {
            return true;
        }
    }

    $cf_visitor = isset($_SERVER['HTTP_CF_VISITOR']) ? $_SERVER['HTTP_CF_VISITOR'] : null;
    if (!is_null($cf_visitor)) {
        try {
            $cf_visitor = json_decode($cf_visitor, true);
            if (is_array($cf_visitor) && array_key_exists('scheme', $cf_visitor)) {
                $cf_visitor['scheme'] = strtolower($cf_visitor['scheme']);
                if ($cf_visitor['scheme'] == 'https') {
                    return true;
                }
            }
        } catch (Exception $e) {}
    }
    return false;
}