I went to a college with that problem. After your mandatory password change, any device autoconnecting to wifi would trigger a lockout. Since the same password was also use to log into network computers, there was no way to visit the webapp to unlock your account.
Unless you had data on your smartphone or had a friend who was logged in, you were SoL.
Unless you had data on your smartphone or had a friend who was logged in, you were SoL.