def headers(auth_token=None):
    """
    Generate an appropriate set of headers given an auth_token.

    :param str auth_token: The auth_token or None.
    :return: A dict of common headers.
    """
    h = {'content-type': ['application/json'],
         'accept': ['application/json'],
         'User-Agent': ['OtterScale/0.0']}

    if auth_token is not None:
        h['x-auth-token'] = [auth_token]

    return h