rails - "WARNING: Can't verify CSRF token authenticity" for json devise requests - ruby-on-rails-3

Question

How can I retrieve the CSRF token to pass with a JSON request?
I know that for security reasons Rails is checking the CSRF token on all the request types (including JSON/XML).
I could put in my controller skip_before_filter :verify_authenticity_token, but I would lose the CRSF protection (not advisable :-) ).
This similar (still not accepted) answer suggests to
Retrieve the token with <%= form_authenticity_token %>
The question is how? Do I need to do a first call to any of my pages to retrieve the token and then do my real authentication with Devise? Or it is an information one-off that I can get from my server and then use consistently (until I manually change it on the server itself)?

Answer 1

EDIT:
In Rails 4 I now use what #genkilabs suggests in the comment below:
protect_from_forgery with: :null_session, if: Proc.new { |c| c.request.format == 'application/json' }
Which, instead of completely turning off the built in security, kills off any session that might exist when something hits the server without the CSRF token.
skip_before_filter :verify_authenticity_token, :if => Proc.new { |c| c.request.format == 'application/json' }
This would turn off the CSRF check for json posts/puts that have properly been marked as such.
For example, in iOS setting the following to your NSURLRequest where "parameters" are your parameters:
[request setHTTPMethod:#"POST"];
[request setValue:#"application/json"
forHTTPHeaderField:#"content-type"];
[request setValue:#"application/json"
forHTTPHeaderField:#"accept"];
[request setHTTPBody:[NSData dataWithBytes:[parameters UTF8String]
length:[parameters length]]];

Answer 2

You can send the CSRF token, after a successful log-in, using a custom header.
E.g, put this in your sessions#create :
response.headers['X-CSRF-Token'] = form_authenticity_token
Sample log-in response header providing the CSRF token:
HTTP/1.1 200 OK
Cache-Control: max-age=0, private, must-revalidate
Connection: Keep-Alive
Content-Length: 35
Content-Type: application/json; charset=utf-8
Date: Mon, 22 Oct 2012 11:39:04 GMT
Etag: "9d719d3b9aabd413c3603e04e8a3933d"
Server: WEBrick/1.3.1 (Ruby/1.9.3/2012-10-12)
Set-Cookie: [cut for readability]
X-Csrf-Token: PbtMPfrszxH6QfRcWJCCyRo7BlxJUPU7HqC2uz2tKGw=
X-Request-Id: 178746992d7aca928c876818fcdd4c96
X-Runtime: 0.169792
X-Ua-Compatible: IE=Edge
This Token is valid until you log-in again or (log-out if you support this through your API).
Your client can extract and store the token from the log-in response headers. Then, each POST/PUT/DELETE request must set the X-CSRF-Token header with the value received at the log-in time.
Sample POST headers with the CSRF token:
POST /api/report HTTP/1.1
Accept: application/json
Accept-Encoding: gzip, deflate, compress
Content-Type: application/json; charset=utf-8
Cookie: [cut for readability]
Host: localhost:3000
User-Agent: HTTPie/0.3.0
X-CSRF-Token: PbtMPfrszxH6QfRcWJCCyRo7BlxJUPU7HqC2uz2tKGw=
Documentation: form_authenticity_token

Answer 3

Indeed simplest way. Don't bother with changing the headers.
Make sure you have:
<%= csrf_meta_tag %>
in your layouts/application.html.erb
Just do a hidden input field like so:
<input name="authenticity_token"
type="hidden"
value="<%= form_authenticity_token %>"/>
Or if you want a jquery ajax post:
$.ajax({
type: 'POST',
url: "<%= someregistration_path %>",
data: { "firstname": "text_data_1", "last_name": "text_data2", "authenticity_token": "<%= form_authenticity_token %>" },
error: function( xhr ){
alert("ERROR ON SUBMIT");
},
success: function( data ){
//data response can contain what we want here...
console.log("SUCCESS, data="+data);
}
});
Basically when you post your json data just add a valid authenticity_token field to the post data and the warning should go away...

Answer 4

I resolved that error this way:
class ApplicationController < ActionController::Base
protect_from_forgery
skip_before_action :verify_authenticity_token, if: :json_request?
protected
def json_request?
request.format.json?
end
end
Source:
http://api.rubyonrails.org/classes/ActionController/RequestForgeryProtection.html

Answer 5

What's worrying is that in Rails 3.2.3 we now get the CSRF warning in production.log but the post does not fail! I want it to fail as it protects me from attacks. And you can add the csrf token with jquery before filter btw:
http://jasoncodes.com/posts/rails-csrf-vulnerability

Answer 6

I have used the below. Using include? so if the content type is application/json;charset=utf-8 then it is still working.
protect_from_forgery with: :null_session, if: Proc.new { |c| c.request.format.include? 'application/json' }

Answer 7

This answer is better.
You get to keep the CSRF-TOKEN validation with no extra effort (the token is appended) before any XMLHttpRequest send. No JQuery, no nothing just copy/paste and refresh.
Simply add this code.
(function() {
var send = XMLHttpRequest.prototype.send,
token = $('meta[name=csrf-token]').attr('content');
XMLHttpRequest.prototype.send = function(data) {
this.setRequestHeader('X-CSRF-Token', token);
return send.apply(this, arguments);
};
}());

Answer 8

I had the same issue with the following version of Rails:
gem 'rails', :git => 'git://github.com/rails/rails.git', :branch => '3-2-stable'
I updated to 3.2.2 and everything works fine for me now. :)
gem 'rails', '3.2.2'

Answer 9

I ran into the same issue tonight.
The reason that happens is because when you sign in the last csrf-token is no longer valid.
What I did was:
$("meta[name=csrf-token]").attr('content', '<%= form_authenticity_token %>'); in your app/views/devise/sessions/create.js.rb.
Now it does have a valid csrf-token :)
I hope it helps

Answer 10

Also for development/test mode.
protect_from_forgery with: :exception unless %w(development test).include? Rails.env
This warning shows because you are using :null_session, in Rails 4.1 it works by default if no with: options specified.
protect_from_forgery