def METHOD_NAME(session, hub_url, user, server_name=""):
    """Stop a server via the JupyterHub API
    Returns when the server has finished stopping
    """
    # step 1: get user status
    user_url = f"{hub_url}/hub/api/users/{user}"
    server_url = f"{user_url}/servers/{server_name}"
    log_name = f"{user}/{server_name}".rstrip("/")
    log.info(f"Stopping server {log_name}")
    r = session.delete(server_url)
    if r.status_code == 404:
        log.info(f"Server {log_name} already stopped")
    r.raise_for_status()
    if r.status_code == 204:
        log.info(f"Server {log_name} stopped")
        return
    # else: 202, stop requested, but not complete
    # wait for stop to finish
    log.info(f"Server {log_name} stopping...")
    # wait for server to be done stopping
    while True:
        r = session.get(user_url)
        r.raise_for_status()
        user_model = r.json()
        if server_name not in user_model.get("servers", {}):
            log.info(f"Server {log_name} stopped")
            return
        server = user_model["servers"][server_name]
        if not server['pending']:
            raise ValueError(f"Waiting for {log_name}, but no longer pending.")
        log.info(f"Server {log_name} pending: {server['pending']}")
        # wait to poll again
        time.sleep(1)