If you can't connect to a public WiFi network - for example at the airport or Internet café - the solution could be very simple. Here's how to fix it on iPhone, iPad and Mac.
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Captive WiFi networks are public WiFi networks that are available upon registration or for a fee. They are the ones you often come across in bars, cafés, hotels, stations, airports and in public places in general.
Usually, you can access them by opening Settings > WiFi and select the network you are interested in, but sometimes -for some reason- the window with the registration (or login) form does not open automatically. We reveal a little trick to always keep on hand, in case the problem arises.
Simply, bookmark this web page in Safari:
After that, open it every time iPhone, iPad or Mac connects to WiFi without showing the registration/login window: this will force it to open. If the Internet connection is already fully functional, the page in question will show the word "Success."