mqtt_client::credentials

Assign credentials that will be used to connect to a Broker.

mqtt_client & credentials(
    std::string client_id,
    std::string username = "",
    std::string password = ""
);

Credentials consist of a unique Client Identifier and, optionally, a User Name and Password.

	Important
	This function takes action when the client is in a non-operational state, meaning the `mqtt_client::async_run` function has not been invoked. Furthermore, you can use this function after the `mqtt_client::cancel` function has been called, before the `mqtt_client::async_run` function is invoked again.