Add Support for Fetch Metadata Request Headers

[meggles711]

I would like to implement Fetch Metadata Request Headers as a new security feature in Django.

What are Fetch Metadata Request Headers?

Fetch metadata request headers are a relatively new security feature used to protect against cross-origin request attacks like CSRF. Browsers that support them provide request origin information to the web server inside headers with every request. This information includes what site is making the request, the mode or type of the request, and the destination of the request. The information provided in the fetch metadata request headers can be used to create a resource isolation policy that protects web application users from cross-origin attacks.

Proposed Changes to Django

New checks should be added to the CSRF middleware. Currently the middleware will check the referer header as one method of determining request validity. When the fetch metadata request headers are set, these should be used for resource isolation checks instead. Otherwise, the policy will fallback on validating with the referer header.

If the fetch metadata headers are set, this resource isolation policy is followed:

Same-site and browser-initiated requests are allowed
Top level navigation (HTTP GET) is allowed
Developer defined endpoints that are meant to serve cross-site traffic are allowed
Reject all other requests

After this policy is followed CSRF processing will continue as normal.

Please provide me some feedback on this implementation plan and let me know if you would like to see this new security feature in Django.

[Mariusz Felisiak]

Fetch metadata request headers are still on an ​early and experimental stage and may change at any moment. Moreover browsers don't support them (e.g. Firefox and Safari). We can reconsider this ticket when the specification becomes more mature and stable.