I'm not really sure how to word this exactly, so hopefully someone can make sense of it. I've been working on an iPad app that syncs files from a server to your iPad and lets you build presentations with the various files. The corporation I'm working with on this app has a wireless network that requires you to re-authenticate every hour. So every hour instead of getting the expected JSON api response, any HTTP request pulls down the page needed to reauth with the wireless network. I was wondering is there is a specific HTTP response code related to getting sent that page or a "best-practice" way of testing for that page as opposed to JSON.
Granted I could just test to see if the response is HTML, but that doesn't account for other redirect responses that I haven't found yet. I could just test part of the HTML to see if it matches a predetermined portion of the html, but I'm an outside contractor. I can't guarantee they won't change the markup or verbiage of the page after I've made my deliverable.
So does anyone out in the ether know a "best practices" methodology for testing if the app needs to reauth before syncing?
I noticed that on Mac OS X and maybe even iOS, when you connect to a new Wi-Fi network, it will try to contact www.apple.com. This is being done to check if the internet connectivity is available. If it's not available, the Captive Network Assistant will pop-up, showing you the authentication page, or sometimes when I'm in Starbucks, an advertisement.
Following your question, since Apple themselves is doing it this way, I think you could check for HTTP response code, look for something in the HTML markup (slightly discouraged though) or trying to connect to a known server (Reachability).
For a corporation practicing well-documented projects, I am quite sure they won't be changing things without making sure that your app, once deployed will continue to work.