How can I disable wireless captive portal support? On a particular wireless network, most internet access is blocked by a captive portal but certain websites are not blocked, e.g.:


http://www.apple.com/ is redirected to a captive portal login page.
http://www.my-university.edu/ is accessible without having to log in.


I want to access a website that is not blocked. When I try to connect, however,


iOS automatically displays the captive portal after connecting.
iOS automatically disconnects after I close the captive portal.


How can I escape this aggressive automation?
As documented in the Apple knowledge base:


  If you cancel before logging in to the network
  
  Tapping Cancel on the Log In screen disassociates the device from the captive Wi-Fi network.
  
  If you joined the network from the Wi-Fi screen using the ⓘ button, or you joined less than eight minutes ago, you'll see a message telling you the network isn't connected to the Internet. You can choose one of these options:
  
  
  Use Without Internet: this option will dismiss the Welcome screen, turn off Auto-Login for the network, keep your device associated with the network, and allow you to interact with the network in other ways.
  Use Other Network: this option will dismiss the Welcome screen, disassociate your device from the network, and return you to the Wi-Fi Settings screen. From there, you can choose a different network.
  Cancel: this option will return you to the Welcome screen.
  


Therefore you can (now—I don't know in which version of iOS this was introduced) click cancel and then "Use Without Internet".