I've noticed my Settings app in iOS 10 crash occasionally when trying to join a wifi network that uses a webpage for credentials (like hotel wifi that needs your room number, or a wifi network that requires a credit card.)
The way we get around this crash when it happens is to tap the info button (circle with an i on the right) and turn off the
auto-login switch. Then open Safari and try to browse to any webpage, and you should get the wifi login page to enter your credentials without a crash.
You may need to tap on the network to join in Settings > Wifi, and then very quickly tap the info "i" button (before the login page gets a chance to pop up) to get the settings to show you the auto-login switch.