Document isCsrfTokenValid

[xabbuh]

see symfony/symfony#11602

[wouterj]

Where should we document this? We have just 2 locations where we talk about CSRF afaik, and both should not have this addition:

1. In book/forms (http://symfony.com/doc/current/book/forms.html#csrf-protection), this talks about build-in Form CSRF support
2. In cookbook/security (http://symfony.com/doc/current/cookbook/security/csrf_in_login_form.html), this talks exclusivly on configuring the security system to use CSRF.

[xabbuh]

I'm not sure when you need this method at all. Isn't CSRF validation performed automatically with the rest of the validation?

[javiereguiluz]

I'll ask @lyrixx, who is the author of this new feature, to better explain us a use case for this feature.

[stof]

The goal is to be able to use CSRF protection in actions where you are not using a Symfony Form (for instance on DELETE actions where doing the whole form binding just for the CSRF protection is way overkill and hurts performance)

[wouterj]

In that case, I would propose to create a new cookbook article in the Controllers section talking about this.