Cross Domain Policy Header Test

The Cross Domain Policy Test tool checks for the presence of cross-domain security policy in the HTTP headers returned by your website. For those who are not aware, the cross-domain headers tell the browser what kind of policy the server has set up for Ajax requests that are not directed from the same domain. “Same domain” in this case means that if the given web page was loaded on mydomain.com, for example, if it sends requests to api.mydomain.com, these requests will be blocked. The same is true for requests sent to mydomain.com:8000, which is not treated as “same domain” because the port is different.

Why you should care?

Restricting browser requests to the same domain is a great idea in Web security. It prevents, for example, malicious scripts from sending information to other domains. That said, it’s not always possible to work within this restriction. Modern applications are deployed as Single Page Applications (SPA), where the frontend is on a completely different domain/port from the server-side of the application. In such cases, having cross-domain headers that tell the browsers to trust some/all domains for incoming requests is a must.

As a result, if these headers are missing (perhaps you forgot them?) the website will stop working for the cross-domain requests.

Check out this implementation guide if you need help in the configuration.