Let's say that an customer or friend comes to my place (shop, hotel, home, restaurant - whatever) and wants to use my guest WiFi network. Voucher system is ok in most cases, but it would be great upgrade to hotspot ease of use to send him one-time access code by e-mail after "one click verification" - something like button "Send code". I know there's Twilio implementation for SMS auth, but requires paid account and for home use it may be unacceptable cost to pay for a mobile numer ($4 in my case) and each message ;-)