How to create WiFi popup login page

Question

When I go to a place with a WiFi hotspot (such as Panera Bread) and connect with my iPhone, the hotspot login page appears as a popup. That is, no matter what app I'm running or what web page I'm on, the login page scrolls up from the bottom, asks for my login credentials, and then disappears.

But at some other hotspots, I don't get the login page until I go to Safari and try to load a web page.

What is the iPhone looking for that causes it to pop up the login page at some hotspots and not others? Is there a special HTML meta tag? Or is it related to the way the redirect is implemented?

Answer 1

I suspect that when the login page pops up the Wi-Fi is using EAP. This is a Wi-Fi protocol for authentication. In the case where you need to go to a web page then the authentication will be a custom access implemented by a server (i.e. at a higher level than EAP).

Answer 2

I managed to find out the correct term for this authentication type: "Captive portal". Punching in Captive Portal iPhone into Google turned out a few technical details from these pages: one, two, three.

To implement a Wi-Fi popup login page:

1. DNS request for www.apple.com must not fail
2. HTTP request for http://www.apple.com/library/test/success.html with special user agent CaptiveNetworkSupport/1.0 wispr must not return Success.

I have not tested this, but it sounds about right.