Image transformation CDN

Design an image-transformation CDN where customers request derivatives via URL parameters (?w=800&fmt=avif&q=70&fit=cover&dpr=2) and the edge generates and caches them on demand. Unlike a fixed thumbnail service, transforms are open-ended and customer-controlled, which creates two problems: an enormous (potentially abusable) cache-key space, and the risk that anyone can hammer your origin with infinite distinct transform URLs. Scale: 200K req/s, hundreds of variants per source image, source images on customer origins.