The Web Applications (WebApps) Working Group and the Web Application Security (WebAppSec) Working Group have published today a Recommendation of Cross-Origin Resource Sharing (CORS). This document defines a mechanism to enable client-side cross-origin requests. Specifications that enable an API to make cross-origin requests to resources can use the algorithms defined by this specification. If such an API is used on http://example.org resources, a resource on http://hello-world.example can opt in using the mechanism described by this specification (e.g., specifying Access-Control-Allow-Origin: http://example.org as response header), which would allow that resource to be fetched cross-origin from http://example.org. Learn more about the Rich Web Client Activity and the Security Activity.