Q:

What information can I get about my iOS customer

I want to know what identifying information I will be able to send to my web server from my iOS app.
I have searched the Apple Developer website to answer this question but I cannot seem to find anything. 
This is the type of information I am interested in:

Unique Identifier
First Name 
Last Name  
Email Address
Age
Address

A:

There is absolutely no information at all about the user of your app available through any public API.
If you want anything you need to provide a form in your app that the user can fill in.
And any app asking for such information will quickly be deleted by a user unless the information is critical to the app's functionality.

