reCAPTCHA and throttling after suspicious number of failed attempts by an IP.
Four digit PIN prompt that gets displayed even when requesting invalid URL. Make PIN verification backend request include some nonce associated with original request, and force nonce to be regenerated if PIN verification fails. PIN is also as easy to communicate verbally as URL.
Four digit PIN prompt that gets displayed even when requesting invalid URL. Make PIN verification backend request include some nonce associated with original request, and force nonce to be regenerated if PIN verification fails. PIN is also as easy to communicate verbally as URL.