Summary:
For methods other than `GET`, `HEAD`, and `OPTIONS`, allow cookie-based authentication only if a certain custom header is present.
Specifically, we check that `X-Requested-With` is set to `XMLHttpRequest`. This is somewhat arbitrary, but allows us to use https://expressjs.com/en/api.html#req.xhr.
A request send from a browser that sets a custom header will prompt a preflight check, giving us a chance to check if the origin is trusted.
This diff deals with getting the header in place. There will be more work to do after this:
* Make sure that all important endpoints are checking origin. Skimming code, /api endpoint check origin, and some but not all others.
* Add tests spot-testing origin checks.
* Check on cases that authenticate differently.
- Check the websocket endpoint - it can be connected to from an arbitrary site; there is per-doc access control but probably better to lock it down more.
- There may be old endpoints that authenticate based on knowledge of a client id rather than cookies.
Test Plan: added a test
Reviewers: dsagal
Reviewed By: dsagal
Differential Revision: https://phab.getgrist.com/D2631
Summary: This moves enough server material into core to run a home server. The data engine is not yet incorporated (though in manual testing it works when ported).
Test Plan: existing tests pass
Reviewers: dsagal
Reviewed By: dsagal
Differential Revision: https://phab.getgrist.com/D2552
