Ionic login with Laravel


I have a working CURD user API which is created using Laravel resource. That REST API is part of Laravel web application. It is using MYSQL database. What I wanna do is to create ionic login using the existing user API. My current concern is that I wanna let users to login once until they actually logout even the ionic app has been closed. I am still confusing with oauth2. Could you please suggest me how I should do?