Login authentication

[lasking88]

The procedure of login authentication is as follows.

1. The user types in login code.
2. Perform get request with login code query.
3. Returns an object including School ID if the code is correct, or error message.

In order to re-login without typing the code again, there are two options with current server.

1. Stores plain login code on the device and use it whenever the app is launched.
   (security problem : whoever is able to access the device can retrieve the plain code.)
   (Since the user has to send plain text, storing hashed code won't work.)
2. Stores the returned status when the code is correct.
   (This causes a problem when the code is changed. Once any user logged in the app, they are able to log in forever even though the code is changed on the server.)

The app is implemented with option 1 temporarily, but it has to be resolved for the security reason.