Detect https correctly when behind a proxy/loadbalancer

[xeli]

The wordpress is_ssl() does not check the HTTP-X-Forwarded-Proto http header to determine if the site is on ssl.

This cause all assets (css/js/images) to be served as http rather than https.

The fix is rather easy in wp-include/functions.php change:

function is_ssl() {
    if ( isset($_SERVER['HTTPS']) ) {
        if ( 'on' == strtolower($_SERVER['HTTPS']) )
            return true;
        if ( '1' == $_SERVER['HTTPS'] )
            return true;
    } elseif ( isset($_SERVER['SERVER_PORT']) && ( '443' == $_SERVER['SERVER_PORT'] ) ) {
        return true;
    }
    return false;
}

to

function is_ssl() {
    if ( isset($_SERVER['HTTPS']) ) {
        if ( 'on' == strtolower($_SERVER['HTTPS']) )
            return true;
        if ( '1' == $_SERVER['HTTPS'] )
            return true;
    } elseif ( isset($_SERVER['SERVER_PORT']) && ( '443' == $_SERVER['SERVER_PORT'] ) ) {
        return true;
    } elseif ( isset($_SERVER['HTTP_X_FORWARDED_PROTO']) && ( $_SERVER['HTTP_X_FORWARDED_PROTO'] == 'https' ) {
        return true;
    }
    return false;
}

[dd32]

#24394 and #19337 and #15733

In particular:
​http://core.trac.wordpress.org/ticket/19337#comment:4