Token Authentication vs. Cookies

Question

What is the difference between token authentication and authentication using cookies?

I am trying to implement the Ember Auth Rails Demo but I do not understand the

Answer 1

A typical web app is mostly stateless, because of its request/response nature. The HTTP protocol is the best example of a stateless protocol. But since most web apps need state, in order to hold the state between server and client, cookies are used such that the server can send a cookie in every response back to the client. This means the next request made from the client will include this cookie and will thus be recognized by the server. This way the server can maintain a session with the stateless client, knowing mostly everything about the app's state, but stored in the server. In this scenario at no moment does the client hold state, which is not how Ember.js works.

In Ember.js things are different. Ember.js makes the programmer's job easier because it holds indeed the state for you, in the client, knowing at every moment about its state without having to make a request to the server asking for state data.

However, holding state in the client can also sometimes introduce concurrency issues that are simply not present in stateless situations. Ember.js, however, deals also with these issues for you; specifically ember-data is built with this in mind. In conclusion, Ember.js is a framework designed for stateful clients.

Ember.js does not work like a typical stateless web app where the session, the state and the corresponding cookies are handled almost completely by the server. Ember.js holds its state completely in Javascript (in the client's memory, and not in the DOM like some other frameworks) and does not need the server to manage the session. This results in Ember.js being more versatile in many situations, e.g. when your app is in offline mode.

Obviously, for security reasons, it does need some kind of token or unique key to be sent to the server everytime a request is made in order to be authenticated. This way the server can look up the send token (which was initially issued by the server) and verify if it's valid before sending a response back to the client.

In my opinion, the main reason why to use an authentication token instead of cookies as stated in Ember Auth FAQ is primarily because of the nature of the Ember.js framework and also because it fits more with the stateful web app paradigm. Therefore the cookie mechanism is not the best approach when building an Ember.js app.

I hope my answer will give more meaning to your question.

Answer 2

Http is stateless. In order to authorize you, you have to "sign" every single request you're sending to server.

Token authentication

• A request to the server is signed by a "token" - usually it means setting specific http headers, however, they can be sent in any part of the http request (POST body, etc.)

• Pros:

  • You can authorize only the requests you wish to authorize. (Cookies - even the authorization cookie are sent for every single request.)
  • Immune to XSRF (Short example of XSRF - I'll send you a link in email that will look like <img src="http://bank.com?withdraw=1000&to=myself" />, and if you're logged in via cookie authentication to bank.com, and bank.com doesn't have any means of XSRF protection, I'll withdraw money from your account simply by the fact that your browser will trigger an authorized GET request to that url.) Note there are anti forgery measure you can do with cookie-based authentication - but you have to implement those.
  • Cookies are bound to a single domain. A cookie created on the domain foo.com can't be read by the domain bar.com, while you can send tokens to any domain you like. This is especially useful for single page applications that are consuming multiple services that are requiring authorization - so I can have a web app on the domain myapp.com that can make authorized client-side requests to myservice1.com and to myservice2.com.
• Cons:
  • You have to store the token somewhere; while cookies are stored "out of the box". The locations that comes to mind are localStorage (con: the token is persisted even after you close browser window), sessionStorage (pro: the token is discarded after you close browser window, con: opening a link in a new tab will render that tab anonymous) and cookies (Pro: the token is discarded after you close the browser window. If you use a session cookie you will be authenticated when opening a link in a new tab, and you're immune to XSRF since you're ignoring the cookie for authentication, you're just using it as token storage. Con: cookies are sent out for every single request. If this cookie is not marked as https only, you're open to man in the middle attacks.)
  • It is slightly easier to do XSS attack against token based authentication (i.e. if I'm able to run an injected script on your site, I can steal your token; however, cookie based authentication is not a silver bullet either - while cookies marked as http-only can't be read by the client, the client can still make requests on your behalf that will automatically include the authorization cookie.)
  • Requests to download a file, which is supposed to work only for authorized users, requires you to use File API. The same request works out of the box for cookie-based authentication.

Cookie authentication

• A request to the server is always signed in by authorization cookie.
• Pros:
  • Cookies can be marked as "http-only" which makes them impossible to be read on the client side. This is better for XSS-attack protection.
  • Comes out of the box - you don't have to implement any code on the client side.
• Cons:
  • Bound to a single domain. (So if you have a single page application that makes requests to multiple services, you can end up doing crazy stuff like a reverse proxy.)
  • Vulnerable to XSRF. You have to implement extra measures to make your site protected against cross site request forgery.
  • Are sent out for every single request, (even for requests that don't require authentication).

Overall, I'd say tokens give you better flexibility, (since you're not bound to single domain). The downside is you have to do quite some coding by yourself.