GHSA-mh55-gqvf-xfwm: Denial of service via malicious preflight requests in github.com/rs/cors

Middleware causes a prohibitive amount of heap allocations when processing malicious preflight requests that include a Access-Control-Request-Headers (ACRH) header whose value contains many commas. This behavior can be abused by attackers to produce undue load on the middleware/server as an attempt to cause a denial of service.