My Login System Idea - How best to execute?

So I’ve created my world and am using the Action RPG Inventory System as out of the box it already does everything I need from it…my question is how do best to execute a login system I have in mind.

So essentially when someone joins the session I want them to be controlling a logged out pawn which is just a camera situated at player start and add the login widget to the viewport. After entering login details, I want a player to spawn in the world with the inventory pawn and inventory character where they left off when they logged out (these details I want to be stored in a text file on the machine running the server for now…once I get some webspace I will most likely use php and mysql).

Are there any resources available for read/write text files, changing player pawns and characters out there I can reference and does this seem like a good way to execute this system?

For text files.

Using Json in Unreal Engine 4 – Part 1

Using Json in Unreal Engine 4 – Part 2