Using CAPTCHA and Challenge in AWS WAF

CAPTCHA – Requires the end user to solve a CAPTCHA puzzle to prove that a human being is sending the request. CAPTCHA puzzles are intended to be fairly easy and quick for humans to complete successfully and hard for computers to either complete successfully or to randomly complete with any meaningful rate of success.

In web ACL rules, CAPTCHA is commonly used when a Block action would stop too many legitimate requests, but letting all traffic through would result in unacceptably high levels of unwanted requests, such as from bots. For information about the rule action behavior, see How the AWS WAFCAPTCHA and Challenge rule actions work.

You can also program a CAPTCHA puzzle implementation in your client application integration APIs. When you do this, you can customize the behavior and placement of the puzzle in your client application. For more information, see Using client application integrations with AWS WAF.

Challenge – Runs a silent challenge that requires the client session to verify that it's a browser, and not a bot. The verification runs in the background without involving the end user. This is a good option for verifying clients that you suspect of being invalid without negatively impacting the end user experience with a CAPTCHA puzzle. For information about the rule action behavior, see How the AWS WAFCAPTCHA and Challenge rule actions work.

The Challenge rule action is similar to the challenge run by the client intelligent threat integration APIs, described at Using client application integrations with AWS WAF.