def x_forwarded_ip(request):
    """
    Returns the IP Address contained in the 'HTTP_X_FORWARDED_FOR' header, if
    present. Otherwise, `None`.

    Should handle properly configured proxy servers.
    """
    ip_address_list = request.META.get('HTTP_X_FORWARDED_FOR')
    if ip_address_list:
        ip_address_list = ip_address_list.split(',')
        return ip_address_list[0]