def METHOD_NAME(lms_callback_url, lms_key, queue_name):
    """
    Generate header for delivery and reply of queue request.
    Xqueue header is a JSON-serialized dict:
        { 'lms_callback_url': url to which xqueue will return the request (string),
          'lms_key': secret key used by LMS to protect its state (string),
          'queue_name': designate a specific queue within xqueue server, e.g. 'MITx-6.00x' (string)
        }
    """
    return json.dumps({
        'lms_callback_url': lms_callback_url,
        'lms_key': lms_key,
        'queue_name': queue_name
    })