import pytz


def http_date(dt):
    """ Convert datetime object into http date according to RFC 1123.

    :param datetime dt: datetime object to convert
    :return: dt as a string according to RFC 1123 format
    :rtype: str
    """
    return dt.astimezone(pytz.utc).strftime('%a, %d %b %Y %H:%M:%S GMT')