AWS WAF introduces dynamic label interpolation for custom request and response handling

Amazon Web Services has launched dynamic label interpolation for AWS WAF, a new feature that allows security engineers to forward WAF classification signals to origin servers and embed contextual information in responses using a single rule. The capability uses ${namespace:} syntax in custom request headers, response headers, and response bodies to forward entire label namespaces at once, eliminating the need for security teams to maintain separate rules for every signal value. For instance, a single rule with a dynamic variable can now forward all IP reputation signals to an application, enabling adaptive responses such as enforcing multi-factor authentication for suspicious traffic. The feature also introduces synthetic labels, which are built-in values resolved from request context including client IP addresses, WAF request IDs, and JA3/JA4 TLS fingerprints. These can be embedded in custom block pages and challenge pages to provide users with reference IDs when reporting false positives, or forwarded to applications for adaptive authentication decisions. The interpolation functionality works with any label namespace, including AWS Managed Rules, AWS Marketplace rule groups, and custom labels, with headers automatically adapting as new labels are added to namespaces. Dynamic label interpolation is now available at no additional cost across all AWS regions where AWS WAF operates, requiring no new API fields or configuration steps for implementation.