Generally Available: Azure Front Door capturing request header, response header, and request query string values as server variables

Azure Front Door introduced [Capture URL path segment in server variable](https://azure.microsoft.com/en-us/updates/?searchterms=azure+front+door+server+variable "https://azure.microsoft.com/en-us/updates/?searchterms=azure+front+door+server+variable") last year. We are now making further enhancements by adding capturing request and response header values and a particular request query string value as server variables for use in the rules engine enable more flexible and dynamic HTTP request manipulations and routing at the edge. This feature is useful for various scenarios, naming a few below: * Populate or modify a response header based on a request header value (e.g., adding the same FQDN in Access-Control-Allow-Origin as the request Origin header). * Rename a response header generated by a cloud provider to a brand-specific one by adding a new response header and deleting the original. * Redirect to a destination host using a value captured from an incoming query string key/value pair. * Unleash different scenarios along with existing conditions and action. Syntax: * Request header: {http\_req\_header\_abc} where 'abc' is the header name. * Response header: {http\_resp\_header\_cde} where 'cde' is the header name. * Query string: {http\_req\_arg\_key1} where 'key1' is the key in the query string. [Learn more](https://learn.microsoft.com/en-us/azure/frontdoor/rule-set-server-variables).