Java - How do I keep a user logged into my site for months?

So you actually want like a "Remember me on this computer" option? Here's a language-agnostic way how you can do it:

First create a DB table with at least cookie_id and user_id columns. If necessary also add a cookie_ttl and ip_lock. The column names speaks for itself I guess.
On first-time login (if necessary only with the "Remember me" option checked), generate a long, unique, hard-to-guess key (which is in no way related to the user) which represents the cookie_id and store this in the DB along with the user_id. Store the cookie_id as cookie value of a cookie with known cookie name, e.g. remember. Give the cookie a long lifetime, e.g. one year.
On every request, check if the user is logged in. If not, then check the cookie value cookie_id associated with the cookie name remember. If it is there and it is valid according the DB, then automagically login the user associated with the user_id and postpone the cookie age again and if any, also the cookie_ttl in DB.

In Java/JSP/Servlet terms, make use of HttpServletResponse#addCookie() to add a cookie and HttpServletRequest#getCookies() to get cookies. You can do all the first-time checking in a Filter which listens on the desired recources, e.g. /* or maybe a bit more restricted.

With regard to sessions, you don't need it here. It has a shorter lifetime than you need. Only use it to put the logged-in user or the "found" user when it has a valid remember cookie. This way the Filter can just check its presence in the session and then don't need to check the cookies everytime.

It's after all fairly straight forward. Good luck.

Well, the original reason I chose OpenID was so someone else could handle as much of the implementation and security of authentication for me.

After looking into OpenID more, it appears there is something called an "Immediate Request" (http://openid.net/specs/openid-authentication-2_0.html#anchor28).

When requesting authentication, the Relying Party MAY request that the OP not interact with the end user. In this case the OP MUST respond immediately with either an assertion that authentication is successful, or a response indicating that the request cannot be completed without further user interaction.

Because of this I think I could just store the user's openID url in the cookie, and use an immediate request to see if the user is authenticated or not. This way I don't have to do anything with my database, or implement any logic for preventing session hijacking of the long-lived cookie.

This method of doing it seems to be the way OpenID suggests to do it with their Relying Party Best Practices document.

Thanks BalusC, do you know of any automagic way all of this could be implemented for me? Or do most sites actually make the database table and logic themselves? I just figured that this is such a common thing to do that it would be built into a library or the language or something.

Kyle 2010-02-02 17:16:36

Sorry, no one comes to mind. But this is all truly doable yourself. If you somehow stucks and/or have questions, just `Ask Question` here :)

BalusC 2010-02-02 17:19:37

-1 This approach is a considerable security risk. It's easy to sniff or otherwise steal cookies and reuse them from anywhere on the web. It's basically session hijacking on steroids.

sfussenegger 2010-02-02 17:41:16

@sfussenegger: How is it different from the normal Servlet `HttpSession` (jsessionid), PHP `$_SESSION` (phpsessionid) and any other session construcs used by other weblanguages/frameworks? I just **explicitly** said "generate a long, unique, hard-to-guess key (which is in no way related to the user)". It's easier to hijack the code used to encrypt the session data and abuse it (especially if it's distributed and/or open source), than to guess/hijack a completely random session key and abuse it. That pissed-like -1 from you makes no utter sense, but if that makes you feel better, be my guest :)

BalusC 2010-02-02 17:51:35

@sfussenegger: I see that you're the other answerer here. How is your own answer more safe? You're basically storing all the sensitive information in a cookie instead of in a DB in server side! Encrypted or not, it's unsafe and may affect **all** users whenever the code logic to encrypt it is hijacked/revealed. Also you may have missed the whole point of `cookie_ttl` and `ip_lock` I mentioned in my answer.

BalusC 2010-02-02 18:04:32

Hi BalusC, I was wondering if you could look over my answer to this question: http://stackoverflow.com/questions/2185951/java-how-do-i-keep-a-user-logged-into-my-site-for-months/2186495#2186495, and let me know if you see any flaws in it?

Kyle 2010-02-02 18:19:30

0 - I've overlooked `cookie_ttl` and `ip_lock` the last time, sorry :) I wouldn't say they speak for themselves though. It's important to check these two *every time* a user is authenticated with a `cookie_id` (which you didn't say explicitly).However, breaking a common symmetrical encryption algorithm like AES or Tripple-DES as you said isn't easier than breaking your random key generator. Additionally, it's easier to identify illegal values as they will result in gibberish after decryption. An illegal `cookie_id` might simply be obsolete.

sfussenegger 2010-02-02 18:25:48

That's certainly an interesting alternative en more suited to the OpenID ideology. I myself however haven't used OpenID in my webapps yet, but after reading one and other I'd say, go for it as described in the document you linked.

BalusC 2010-02-02 18:33:06

that's probably the best answer

sfussenegger 2010-02-02 18:33:39

ansaurus

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Java - How do I keep a user logged into my site for months?

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