How to create and manage login session in iOS

1] In login page , if Login is Successful then i stored my Username & Password in NSUserDefault
as follows
Onclick of Login Button.

 NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];
     [defaults setObject:userNameText forKey:@"username"];               
     [defaults setObject:passWordText forKey:@"password"];
     [defaults synchronize];

// Redirected to another viewController .

2] if user click Logout then  Delete All Data as follows.
Onclick of LogOut Button.

 NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];
    [defaults removeObjectForKey:@"username"];
    [defaults removeObjectForKey:@"password"];
    [defaults synchronize];

 // Redirected to Main viewController or Login viewController .

And then

3] in case when user close app and  second time open app at that time , then we need to  check wheather username & password stored in NSUserDefault During ViewDidAppearof Loginpage.
ViewDidAppear of Loginpage.

   NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];

    // check if user Login already

    if([defaults objectForKey:@"username"]!=nil  && ![[defaults objectForKey:@"username"] isEqualToString:@""])

    {

        // Redirected to viewController.

  

    }