Ability for Fairings to respond to requests

[jprider63]

Is your feature request motivated by a concrete problem? Please describe.

I'm attempting to extend rocket_csrf with the ability to automatically check whether valid CSRF tokens are provided in headers. If an invalid token is provided for a write request, I would like the fairing to respond with a permission denied error, but the API does not allow this.

I understand that the philosophy is to respond to requests via request guards or response callbacks, however I believe fairings are the right place for this functionality since this needs to be run on every request. Otherwise, users would need to remember to add request guards to every request and failure to do so would be a security issue.

Why this feature can't or shouldn't live outside of Rocket

The Fairing trait does not give us the ability to abort requests via on_request.

Ideal Solution

Update on_request to give us the ability to respond to requests. Maybe the return type should be something like Option<rocket::request::Outcome>.

Alternatives Considered

The only other approach I've seen to do this is to modify the request to point to a handler defined by the fairing. I'll probably do this for now, but it seems like a hack.

[SergioBenitez]

This is planned. See #749. Indeed, the workaround, well, works, but is unfortunate.

[jprider63]

Thanks! Let me know if I can help with the design or implementation.