应用程序到服务器安全性：如何验证服务器上的Android应用程序/用户？

I am building an app that will not use a login. It involves users making requests to a server where information is stored, and that information can then be sent to other users via HTTP post. What I am wondering is how can I ensure that post requests going to the server are coming from the app and not from some other device sending artificial posts?I am building an app that will not use a login.