When you sign in using Parse, [PFUser currentUser] is cached locally on the device. I have a problem in that some custom data stored in that user's object can be updated outside of the app, so if the user is still logged in calling [PFUser currentUser] will get the cached user object and therefore it won't have the new data. To update the cached user's object, the user has to sign out and back in.
How can I update/refetch the current user programmatically without discarding their session?
Yes, it did have method to deal with this issue from Parse.com. You can check the category of fetch method like - (BFTask *)fetchInBackground and here is the link for API: https://parse.com/docs/ios/api/Classes/PFObject.html#//api/name/fetchInBackground