How does Cloudflare's 'Challenge-Response' mechanism work in detecting and mitigating DDoS attacks?

Cloudflare uses challenge-response mechanisms to verify that a visitor is a legitimate human and not a bot. A common method is to send a CAPTCHA challenge to the user and require them to solve it. This helps distinguish between automated bots that are common in DDoS attacks and real users. The frequency of challenges and the difficulty of the challenge are dynamically adjusted based on the detected traffic patterns.