php - Cookie and session in "remember me" feature

Question

I have never wanted to allow a user to stay logged in for any length of time so I never saw a use for a "remember me" feature. I started thinking about how it's done though and would like some clarification.

I'm currently storing my sessions in a database. What has always perplexed me was how, even though I do not explicitly set a cookie, one is placed in my browser. I'm a little confused because a session is a session and a cookie is a cookie. I don't see how a session sets a cookie.

I'd also like to know if, simply setting another session variable in the session array to keep the user logged in, would be sufficient or would I still need to set a cookie?

Answer 1

In order to pull the session data back from your database a key is needed. This is called the Session ID.

The session ID needs to be stored somewhere. Either as part of the URL string that the client posts back or, more commonly, in a cookie on the client. When the request is posted, session reads the value from the cookie and knows which record to pull back from session storage.

This happens automatically.

The only reason to use session is if the data you want to keep is greater than 4KB (browser limitations); or if the time required to pull the data from your server is greater than reading it from session storage.

If the amount of data you are storing is less than 4KB I would highly recommend you just set that in the cookie to begin with. I generally store things like the user id, user first name, and a couple other attributes. Bear in mind that it is trivial to inspect a cookies value, so this information should be encrypted prior to going to the client.

Another thing is if the query time to pull the data you need from the original source is small, then elect to do that instead of placing it in session. That way you only get it when you actually need it instead of with every single page load.

Answer 2

What has always perplexed me was how, even though I do not explicitly set a cookie, one is placed in my browser.

A session handler has to identify which session belongs to which user.

The vast majority of session libraries do this by setting a cookie.

(Is) setting another session variable in the session array to keep the user logged in would be sufficient or would I still need to set a cookie?

Most session libraries set session cookies. These are cookies without a specified expiry time. They expire when the browser closes and are not sufficient to implement a "Remember Me" feature (which is expected to persist across browser restarts, so must have an explicit expiry time).

Answer 3

Explaining the relationship between Cookie and Session:

PHP uses Cookie to uniquely identify the session for each user. That's the only more reliable way because cookie is sent each time you request a file from the server. Using the token in the cookie, which is also the Session identifier, PHP will look up the tmp directory to see if the session exists. If the session exists, the variables are loaded from the correct file and you will be able to access the variables on that session.

Therefore, cookies store the session identifier which is required to identify which user uses which session. This is also how Session Hijacking come about, when people can change the session identifying cookie to use another person's session identifier.

Answer 4

The underlying PHP session implementation sets the cookie. You can alter this and have the session ID value passed in the query string, but I don't recommend it. You don't use the cookie, PHP does. It references the session ID value stored in the cookie to perform lookups to session data.

I'd also like to know, if simply setting another session variable in the session array to keep the user logged in would be sufficient or would I still need to set a cookie?

As soon as the user closes the browser, the session is killed and the cookie is deleted. I don't believe any mechanism exits to persist the session value, and for good reason.