As much as I understand, web developer should create token and put it in hidden field of form to prevent CSRF attacks. Also, he should save the same token in a session and then, when form is submitted – check that tokens are equal.
I came to question… is it necessary to do this technique for all forms? I mean, imagine form that is created to sign-in. I can’t see any harm done to site and/or user if there is no CSRF protection, because user have no privileges (like he would have if he would be signed-in). The same goes for sign-up… Am I right?
P.S. If I’m wrong, please explain me the concept.
Generally speaking, you want to protect your form anytime its submission will result in a change of content/state; be it adding it, removing it, editing it or sharing it with an external source (“share on xyz !”).
An exemple of forms you wouldn’t need to protect is a search box, since it doesn’t result in any change of content.
If you’re unsure, any form which will result in something being saved/deleted (whether it’s on your site or not) should be protected.
And if you are really unsure just add the token, doesn’t cost anything to be safe.