In the current version of QuickBlox software it is not possible to store application session via REST.
If the application is closed the session will be lost and user will need to log in again.
This kind of access token is needed to read the app data. Has only READ access to resources. The expiration time after the last REST API request is 2 hours.
Currently you can only store login and password in the application.
Also keep in mind that expiration time for token is 2 hours after the last query (this is used for security reasons).
If you perform the query with expiration token you will receive the "Required session does not exist" error. In this case you need to re-create the session.
You can find more information here: Authentication | Server API