iOS - 修改网站上的变量以最终解析数据

I want to make an app for this website: https://my.iusd.org/LoginParent.aspx

I wanted someone to just list the steps that I need to take to make an app that will let the user enter a username, password on the iDevice, and then pass those variables from the iDevice to that site ,so that if the authentication is correct, I can parse the data once the user logs in to show his or her grades.

If I need to make a separate php script to modify/pass variables to the site, how can I run the script for free without having to manage a server?

Thanks in advance.