It depends on which network you're connecting to. If you're logging in to WiFi at your school, you typically use your student username and password. If you're logging in to WiFi at your health care provider's location, you might use your medical username and password (if your health care provider uses this feature). It's different for every network. Your best option is to contact the IT help desk or ask someone who works at that location (could be your landlord, a receptionist, etc.)
BTW, the reason some networks require log-in is to prevent the general public from overloading their network.
09-07-2015 02:06 PM