I just released the Starter Class of "Learn Spring Security":
This tutorial will show how to enable and configure Remember Me functionality in a web application with Spring Security. Setting up the MVC application with security and a simple form login has already been discussed.
The mechanism will be able to identify the user across multiple sessions – so the first thing to understand is that Remember Me only kicks in after the session times out. By default, this happens after 30 minutes of inactivity, but timeout can be configured in the web.xml.
2. The Security XML Configuration
The security namespace will be used to configure the mechanism entirely:
<?xml version="1.0" encoding="UTF-8"?> <beans:beans xmlns="http://www.springframework.org/schema/security" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:beans="http://www.springframework.org/schema/beans" xsi:schemaLocation=" http://www.springframework.org/schema/security http://www.springframework.org/schema/security/spring-security-4.0.xsd http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-4.2.xsd"> <http use-expressions="true"> <intercept-url pattern="/anonymous*" access="isAnonymous()" /> <intercept-url pattern="/login*" access="permitAll" /> <intercept-url pattern="/**" access="isAuthenticated()" /> <form-login login-page='/login.html' authentication-failure-url="/login.html?error=true" /> <logout delete-cookies="JSESSIONID" /> <remember-me key="uniqueAndSecret"/> </http> <authentication-manager> <authentication-provider> <user-service> <user name="user1" password="user1Pass" authorities="ROLE_USER" /> <user name="admin1" password="admin1Pass" authorities="ROLE_ADMIN" /> </user-service> </authentication-provider> </authentication-manager> </beans:beans>
As you can see, the basic configuration using <remember-me> element is extremely simple while remaining very flexible though additional namespace options. The key is important here – it is a private value secret for the entire application and it will be used when generating the contents of the token.
Additionally, the time the token is valid can be configured from the default of 2 weeks to – for example – one day:
<remember-me key="uniqueAndSecret" token-validity-seconds="86400"/>
3. The Login form
The login form is similar to the one we used for form login:
<html> <head></head> <body> <h1>Login</h1> <form name='f' action="login" method='POST'> <table> <tr> <td>User:</td> <td><input type='text' name='username' value=''></td> </tr> <tr> <td>Password:</td> <td><input type='password' name='password' /></td> </tr> <tr> <td>Remember Me:</td> <td><input type="checkbox" name="remember-me" /></td> </tr> <tr> <td><input name="submit" type="submit" value="submit" /></td> </tr> </table> </form> </body> </html>
Notice the newly added checkbox input – mapping to remember-me. This added input is enough to log in with remember me active.
Unfortunately this default path cannot be changed via the namespace in Spring 3.1 – the option is available starting with Spring 3.2 – as follows:
<remember-me remember-me-parameter="custom-remember-me" />
4. The Cookie
The mechanism will create an additional cookie – the “remember-me” cookie – when the user logs in.
The Remember Me cookie contains the following data:
- username – to identify the logged in principal
- expirationTime – to expire the cookie; default is 2 weeks
- MD5 hash – of the previous 2 values – username and expirationTime, plus the password and the predefined key
First thing to notice here is that both the username and the password are part of the cookie – this means that, if either is changed, the cookie is no longer valid. Also, the username can be read from the cookie.
Additionally, it is important to understand that this mechanism is potentially vulnerable if the remember me cookie is captured. The cookie will be valid and usable until it expires or the credentials are changed.
5. In Practice
To easily see the remember me mechanism working, you can:
- log in with remember me active
- wait for the session to expire (or remove the JSESSIONID cookie in the browser)
- refresh the page
Without remember me active, after the cookie expires the user should be redirected back to the login page. With remember me, the user now stays logged in with the help of the new token/cookie.
This tutorial showed how to set up and configure Remember Me functionality in the security configuration, and briefly described what kind of data goes into the cookie.
The implementation can be found in the example github project – this is an Eclipse based project, so it should be easy to import and run as it is.
When the project runs locally, the login.html can be accessed on localhost.