将PHP脚本与android post请求一起使用

I'm using PHP scripts to handle the data I send from an android application as well as the data received from computers. My questions are as follow:

  • If I use a php script using session variables how does that affect the request obtained from the android?
  • Should I use separated php scripts while developing for android although they are meant to do the same?
  • Is it safe to store and send "confidential" data like user id in the android device? (sharedPreferences).

Thank you for your help