def generate_db_auth_token(DBHostname=None, Port=None, DBUsername=None,
    Region=None):
    """
    Generates an auth token used to connect to a db with IAM credentials.
    
    :type DBHostname: str
    :param DBHostname: The hostname of the database to connect to.

    :type Port: int
    :param Port: The port number the database is listening on.

    :type DBUsername: str
    :param DBUsername: The username to log in as.

    :type Region: str
    :param Region: The region the database is in. If None, the client
            region will be used.

    """
    pass
