How does cookie based authentication work?
To expand on Conor's answer and add a little bit more to the discussion...
Can someone give me a step by step description of how cookie based authentication works? I've never done anything involving either authentication or cookies. What does the browser need to do? What does the server need to do? In what order? How do we keep things secure?
Step 1: Client > Signing up
Before anything else, the user has to sign up. The client posts a HTTP request to the server containing his/her username and password.
Step 2: Server > Handling sign up
The server receives this request and hashes the password before storing the username and password in your database. This way, if someone gains access to your database they won't see your users' actual passwords.
Step 3: Client > User login
Now your user logs in. He/she provides their username/password and again, this is posted as a HTTP request to the server.
Step 4: Server > Validating login
The server looks up the username in the database, hashes the supplied login password, and compares it to the previously hashed password in the database. If it doesn't check out, we may deny them access by sending a 401 status code and ending the request.
Step 5: Server > Generating access token
If everything checks out, we're going to create an access token, which uniquely identifies the user's session. Still in the server, we do two things with the access token:
- Store it in the database associated with that user
- Attach it to a response cookie to be returned to the client. Be sure to set an expiration date/time to limit the user's session
Henceforth, the cookies will be attached to every request (and response) made between the client and server.
Step 6: Client > Making page requests
Back on the client side, we are now logged in. Every time the client makes a request for a page that requires authorization (i.e. they need to be logged in), the server obtains the access token from the cookie and checks it against the one in the database associated with that user. If it checks out, access is granted.
This should get you started. Be sure to clear the cookies upon logout!
A cookie is basically just an item in a dictionary. Each item has a key and a value. For authentication, the key could be something like 'username' and the value would be the username. Each time you make a request to a website, your browser will include the cookies in the request, and the host server will check the cookies. So authentication can be done automatically like that.
To set a cookie, you just have to add it to the response the server sends back after requests. The browser will then add the cookie upon receiving the response.
There are different options you can configure for the cookie server side, like expiration times or encryption. An encrypted cookie is often referred to as a signed cookie. Basically the server encrypts the key and value in the dictionary item, so only the server can make use of the information. So then cookie would be secure.
A browser will save the cookies set by the server. In the HTTP header of every request the browser makes to that server, it will add the cookies. It will only add cookies for the domains that set them. Example.com can set a cookie and also add options in the HTTP header for the browsers to send the cookie back to subdomains, like sub.example.com. It would be unacceptable for a browser to ever sends cookies to a different domain.