Which URL does Apple request when connecting to a Wi-Fi network to look for redirects?
I found it. Apple uses http://www.apple.com/library/test/success.html

More information can be found at http://blog.erratasec.com/2010/09/apples-secret-wispr-request.html#.VLA9UsabLOY

The advantage of using a no redirect URL is that you can determine which state you are in:


Connected
Connected to Wi-Fi but Internet is inaccessible due to Wi-Fi router requiring user intervention.
Not connected


These are called captive portals, or, as Apple calls them, captive networks:


  Captive networks (often used in hotels, coffee shops, and other public places) may intercept your software’s HTTP requests and provide a login page instead of the expected data.