def fetch_metadata(url):
    """
    Return a dictionary of OpenGraph metadata found in HTML of given url
    """
    url = url
    base_url = "https://opengraph.lewagon.com/"
    params = dict()
    params["url"] = url

    r = requests.get(base_url, params=params)
    response = r.json()
    if r'site_name' in response.keys():
        description = response['data']['site_name']
        title = response['data']['title']
        return [title, description]
    else:
        return [None,,None]