如何使用Swift删除Logout按钮并永久存储会话FBSDK IOS

I am creating an app in which user can Sign in using Facebook. I am fetching user info like profile picture Username etc. Now when i tap on Login with facebook button FB ask for permission i am loged in. but then there is Logout Button displaying at the same place as LoginWithFacebook button was. I want to Remove the logout button because i do not want the user to log out. I want to store the session and use it all the way long until app is unintsalled because I do not want the user to login each time when he opens the app. This is my code so farI am creating an app in which user can Sign in