Upon entering a Wifi Captive Portal:

When using an Android phone, the top of the screen always displays a fixed "Sign In to [WifiAP name]" text and then below the URL string it used to check for connectivity. With an iPhone it displays three lines of fixed text starting with the URL "captive.apple.com" followed by the Wifi AP name and then "Log In".

Does anybody know how do change those fixed texts? My captive portal is a .html page with some javascript. Many thanks.