Is this Rails JSON authentication API (using Devise) secure? - ruby-on-rails

Question

My Rails app uses Devise for authentication. It has a sister iOS app, and users can log in to the iOS app using the same credentials that they use for the web app. So I need some kind of API for authentication.
Lots of similar questions on here point to this tutorial, but it seems to be out-of-date, as the token_authenticatable module has since been removed from Devise and some of the lines throw errors. (I'm using Devise 3.2.2.) I've attempted to roll my own based on that tutorial (and this one), but I'm not 100% confident in it - I feel like there may be something I've misunderstood or missed.
Firstly, following the advice of this gist, I added an authentication_token text attribute to my users table, and the following to user.rb:
before_save :ensure_authentication_token
def ensure_authentication_token
if authentication_token.blank?
self.authentication_token = generate_authentication_token
end
end
private
def generate_authentication_token
loop do
token = Devise.friendly_token
break token unless User.find_by(authentication_token: token)
end
end
Then I have the following controllers:
api_controller.rb
class ApiController < ApplicationController
respond_to :json
skip_before_filter :authenticate_user!
protected
def user_params
params[:user].permit(:email, :password, :password_confirmation)
end
end
(Note that my application_controller has the line before_filter :authenticate_user!.)
api/sessions_controller.rb
class Api::SessionsController < Devise::RegistrationsController
prepend_before_filter :require_no_authentication, :only => [:create ]
before_filter :ensure_params_exist
respond_to :json
skip_before_filter :verify_authenticity_token
def create
build_resource
resource = User.find_for_database_authentication(
email: params[:user][:email]
)
return invalid_login_attempt unless resource
if resource.valid_password?(params[:user][:password])
sign_in("user", resource)
render json: {
success: true,
auth_token: resource.authentication_token,
email: resource.email
}
return
end
invalid_login_attempt
end
def destroy
sign_out(resource_name)
end
protected
def ensure_params_exist
return unless params[:user].blank?
render json: {
success: false,
message: "missing user parameter"
}, status: 422
end
def invalid_login_attempt
warden.custom_failure!
render json: {
success: false,
message: "Error with your login or password"
}, status: 401
end
end
api/registrations_controller.rb
class Api::RegistrationsController < ApiController
skip_before_filter :verify_authenticity_token
def create
user = User.new(user_params)
if user.save
render(
json: Jbuilder.encode do |j|
j.success true
j.email user.email
j.auth_token user.authentication_token
end,
status: 201
)
return
else
warden.custom_failure!
render json: user.errors, status: 422
end
end
end
And in config/routes.rb:
namespace :api, defaults: { format: "json" } do
devise_for :users
end
I'm out of my depth a bit and I'm sure there's something here that my future self will look back on and cringe (there usually is). Some iffy parts:
Firstly, you'll notice that Api::SessionsController inherits from Devise::RegistrationsController whereas Api::RegistrationsController inherits from ApiController (I also have some other controllers such as Api::EventsController < ApiController which deal with more standard REST stuff for my other models and don't have much contact with Devise.) This is a pretty ugly arrangement, but I couldn't figure out another way of getting access the methods I need in Api::RegistrationsController. The tutorial I linked to above has the line include Devise::Controllers::InternalHelpers, but this module seems to have been removed in more recent versions of Devise.
Secondly, I've disabled CSRF protection with the line skip_before_filter :verify_authentication_token. I have my doubts about whether this is a good idea - I see a lot of conflicting or hard to understand advice about whether JSON APIs are vulnerable to CSRF attacks - but adding that line was the only way I could get the damn thing to work.
Thirdly, I want to make sure I understand how authentication works once a user has signed in. Say I have an API call GET /api/friends which returns a list of the current user's friends. As I understand it, the iOS app would have to get the user's authentication_token from the database (which is a fixed value for each user that never changes??), then submit it as a param along with every request, e.g. GET /api/friends?authentication_token=abcdefgh1234, then my Api::FriendsController could do something like User.find_by(authentication_token: params[:authentication_token]) to get the current_user. Is it really this simple, or am I missing something?
So for anyone who's managed to read all the way to the end of this mammoth question, thanks for your time! To summarise:
Is this login system secure? Or is there something I've overlooked or misunderstood, e.g. when it comes to CSRF attacks?
Is my understanding of how to authenticate requests once users are signed in correct? (See "thirdly..." above.)
Is there any way this code can be cleaned up or made nicer? Particularly the ugly design of having one controller inherit from Devise::RegistrationsController and the others from ApiController.
Thanks!

Answer 1

You don't want to disable CSRF, I have read that people think it doesn't apply to JSON APIs for some reason, but this is a misunderstanding. To keep it enabled, you want to make a few changes:
on there server side add a after_filter to your sessions controller:
after_filter :set_csrf_header, only: [:new, :create]
protected
def set_csrf_header
response.headers['X-CSRF-Token'] = form_authenticity_token
end
This will generate a token, put it in your session and copy it in the response header for selected actions.
client side (iOS) you need to make sure two things are in place.
your client needs to scan all server responses for this header and retain it when it is passed along.
... get ahold of response object
// response may be a NSURLResponse object, so convert:
NSHTTPURLResponse *httpResponse = (NSHTTPURLResponse*)response;
// grab token if present, make sure you have a config object to store it in
NSString *token = [[httpResponse allHeaderFields] objectForKey:#"X-CSRF-Token"];
if (token)
[yourConfig setCsrfToken:token];
finally, your client needs to add this token to all 'non GET' requests it sends out:
... get ahold of your request object
if (yourConfig.csrfToken && ![request.httpMethod isEqualToString:#"GET"])
[request setValue:yourConfig.csrfToken forHTTPHeaderField:#"X-CSRF-Token"];
Final piece of the puzzle is to understand that when logging in to devise, two subsequent sessions/csrf tokens are being used. A login flow would look like this:
GET /users/sign_in ->
// new action is called, initial token is set
// now send login form on callback:
POST /users/sign_in <username, password> ->
// create action called, token is reset
// when login is successful, session and token are replaced
// and you can send authenticated requests

Answer 2

Your example seems to mimic the code from the Devise blog - https://gist.github.com/josevalim/fb706b1e933ef01e4fb6
As mentioned in that post, you are doing it similar to option 1, which they say is the insecure option. I think the key is that you don't want to simply reset the authentication token every time the user is saved. I think the token should be created explicitly (by some kind of TokenController in the API) and should expire periodically.
You'll notice I say 'I think' since (as far as I can tell) nobody has any more information on this.

Answer 3

The top 10 most common vulnerablites in web applications are documented in the OWASP Top 10. This question mentioned that Cross-Site Request Forgery(CSRF) protection was disabled, and CSRF is on the OWASDP Top 10. In short, CSRF is used by attackers to perform actions as an authenticated user. Disabling CSRF protection will lead to high risk vulnerabilities in an application, and undermines the purpose of having a secure authentication system. Its likely that the CSRF protection was failing, because the client is failing to pass the CSRF synchronization token.
Read the entire OWASP top 10, failing to do so is extremely hazardous. Pay close attention to Broken Authentication and Session Management, also check out the Session Management Cheat Sheet.