Add CSRF token to GraphiQL view

[cellis]

This change adds a getCSRFToken method that if provided can be invoked with the request to get a CSRF token for example: req.csrfToken().

This is needed for securing the GraphiQL views (especially on production instances!). I'm using a modified version of this in development to allow my csrf strategy to work. Let me know what you think!

[tothandras]

Thanks for the PR! Can you add support for the other frameworks too (koa, hapi)?

[cellis]

@tothandras I'll look at these other frameworks soon

[phra]

any updates on this?

[cellis]

@phra sorry for the delay. I don't have time to work on this anymore, as I've moved on to using another library. Perhaps someone else is interested in taking this to the finish line by implementing @tothandras' request to add koa and hapi support?

[phra]

@cellis which library are you using? i'm using this one right now.