I'm a newbie when it comes to information security. So pardon me if the solution can be found at page 12 of any introductory text.
I have an express server and two android apps(for clients and admin). The installed apps will ask the user for registration (using a code sent to them by the admin, generated by the server). After registration, the client app will be assigned an id and they will regularly send some data to the server. The communication between apps and server is being done using
How do I verify that the data coming to the server is valid?