def passthrough_challenge_decider(environ, status, headers):
    """ Don't challenge for pre-challenged responses.

    o Assume responsese with 'WWW-Authenticate' or an HTML content type
      are pre-challenged.
    """
    if not status.startswith('401 '):
        return False
    h_dict = dict(headers)
    if 'WWW-Authenticate' in h_dict:
        return False
    ct = h_dict.get('Content-Type')
    if ct is not None:
        return not ct.startswith('text/html')
    return True
