def list_users(contact_points=None, port=None, cql_user=None, cql_pass=None):
    '''
    List existing users in this Cassandra cluster.

    :param contact_points: The Cassandra cluster addresses, can either be a string or a list of IPs.
    :type  contact_points: str | list[str]
    :param port:           The Cassandra cluster port, defaults to None.
    :type  port:           int
    :param cql_user:       The Cassandra user if authentication is turned on.
    :type  cql_user:       str
    :param cql_pass:       The Cassandra user password if authentication is turned on.
    :type  cql_pass:       str
    :return:               The list of existing users.
    :rtype:                dict

    CLI Example:

    .. code-block:: bash

        salt 'minion1' cassandra_cql.list_users

        salt 'minion1' cassandra_cql.list_users contact_points=minion1
    '''
    query = "list users;"

    ret = {}

    try:
        ret = cql_query(query, contact_points, port, cql_user, cql_pass)
    except CommandExecutionError:
        log.critical('Could not list users.')
        raise
    except BaseException as e:
        log.critical('Unexpected error while listing users: %s', e)
        raise

    return ret
List existing users in this Cassandra cluster.

    :param contact_points: The Cassandra cluster addresses, can either be a string or a list of IPs.
    :type  contact_points: str | list[str]
    :param port:           The Cassandra cluster port, defaults to None.
    :type  port:           int
    :param cql_user:       The Cassandra user if authentication is turned on.
    :type  cql_user:       str
    :param cql_pass:       The Cassandra user password if authentication is turned on.
    :type  cql_pass:       str
    :return:               The list of existing users.
    :rtype:                dict

    CLI Example:

    .. code-block:: bash

        salt 'minion1' cassandra_cql.list_users

        salt 'minion1' cassandra_cql.list_users contact_points=minion1