Rails, Devise authentication, CSRF issue

Question

I\'m doing a singe-page application using Rails. When signing in and out Devise controllers are invoked using ajax. The problem I\'m getting is that when I 1) sign in 2) sig

Answer 1

I've just run into this problem as well. There's a lot going on here.

TL;DR - The reason for the failure is that the CSRF token is associated with your server session (you've got a server session whether you're logged in or logged out). The CSRF token is included in the DOM your page on every page load. On logout, your session is reset and has no csrf token. Normally, a logout redirects to a different page/action, which gives you a new CSRF token, but since you're using ajax, you need to do this manually.

• You need to override the Devise SessionController::destroy method to return your new CSRF token.
• Then on the client side you need to set a success handler for your logout XMLHttpRequest. In that handler you need to take this new CSRF token from the response and set it in your dom: $('meta[name="csrf-token"]').attr('content', )

More Detailed Explanation You've most likely got protect_from_forgery set in your ApplicationController.rb file from which all of your other controllers inherit (this is pretty common I think). protect_from_forgery performs CSRF checks on all non-GET HTML/Javascript requests. Since Devise Login is a POST, it performs a CSRF Check. If a CSRF Check fails then the user's current session is cleared, i.e., logs the user out, because the server assumes it's an attack (which is the correct/desired behavior).

So assuming you're starting in a logged out state, you do a fresh page load, and never reload the page again:

1. On rendering the page: the server inserts the CSRF Token associated with your server session into the page. You can view this token by running the following from a javascript console in your browser$('meta[name="csrf-token"]').attr('content').

2. You then Sign In via an XMLHttpRequest: Your CSRF Token remains unchanged at this point so the CSRF Token in your Session still matches the one that was inserted into the page. Behind the scenes, on the client side, jquery-ujs is listening for xhr's and setting a 'X-CSRF-Token' header with the value of $('meta[name="csrf-token"]').attr('content') for you automatically (remember this was the CSRF Token set in step 1 by the sever). The server compares the Token set in the header by jquery-ujs and the one that is stored in your session information and they match so the request succeeds.

3. You then Log Out via an XMLHttpRequest: This resets session, gives you a new session without a CSRF Token.

4. You then Sign In again via an XMLHttpRequest: jquery-ujs pulls the CSRF token from the value of $('meta[name="csrf-token"]').attr('content'). This value is still your OLD CSRF token. It takes this old token and uses it to set the 'X-CSRF-Token'. The server compares this header value with a new CSRF token that it adds to your session, which is different. This difference causes the protect_form_forgery to fail, which throws the WARNING: Can't verify CSRF token authenticity and resets your session, which logs the user out.

5. You then make another XMLHttpRequest that requires a logged in user: The current session doesn't have a logged in user so devise returns a 401.

Update: 8/14 Devise logout does not give you a new CSRF token, the redirect that normally happens after a logout gives you a new csrf token.