The SessionManagementFilter checks the contents of the SecurityContextRepository against the current contents of the SecurityContextHolder to determine whether a user has been authenticated during the current request, typically by a non-interactive authentication mechanism, such as pre-authentication or remember-me ^[17]. If the repository contains a security context, the filter does nothing. If it doesn’t, and the thread-local SecurityContext contains a (non-anonymous) Authentication object, the filter assumes they have been authenticated by a previous filter in the stack. It will then invoke the configured SessionAuthenticationStrategy.

If the user is not currently authenticated, the filter will check whether an invalid session ID has been requested (because of a timeout, for example) and will invoke the configured`InvalidSessionStrategy`, if one is set. The most common behaviour is just to redirect to a fixed URL and this is encapsulated in the standard implementation`SimpleRedirectInvalidSessionStrategy`. The latter is also used when configuring an invalid session URL through the namespace,as described earlier.

SessionAuthenticationStrategy is used by both SessionManagementFilter and AbstractAuthenticationProcessingFilter, so if you are using a customized form-login class, for example, you will need to inject it into both of these. In this case, a typical configuration, combining the namespace and custom beans might look like this:

<http>
<custom-filter position="FORM_LOGIN_FILTER" ref="myAuthFilter" />
<session-management session-authentication-strategy-ref="sas"/>
</http>

<beans:bean id="myAuthFilter" class=
"org.springframework.security.web.authentication.UsernamePasswordAuthenticationFilter">
	<beans:property name="sessionAuthenticationStrategy" ref="sas" />
	...
</beans:bean>

<beans:bean id="sas" class=
"org.springframework.security.web.authentication.session.SessionFixationProtectionStrategy" />

Note that the use of the default, SessionFixationProtectionStrategy may cause issues if you are storing beans in the session which implement HttpSessionBindingListener, including Spring session-scoped beans. See the Javadoc for this class for more information.

Spring Security is able to prevent a principal from concurrently authenticating to the same application more than a specified number of times. Many ISVs take advantage of this to enforce licensing, whilst network administrators like this feature because it helps prevent people from sharing login names. You can, for example, stop user"Batman" from logging onto the web application from two different sessions. You can either expire their previous login or you can report an error when they try to log in again, preventing the second login. Note that if you are using the second approach, a user who has not explicitly logged out (but who has just closed their browser, for example) will not be able to log in again until their original session expires.

Concurrency control is supported by the namespace, so please check the earlier namespace chapter for the simplest configuration. Sometimes you need to customize things though.

The implementation uses a specialized version of SessionAuthenticationStrategy, called ConcurrentSessionControlAuthenticationStrategy.

To use concurrent session support, you’ll need to add the following to web.xml:

<listener>
	<listener-class>
	  org.springframework.security.web.session.HttpSessionEventPublisher
	</listener-class>
</listener>

In addition, you will need to add the ConcurrentSessionFilter to your FilterChainProxy. The ConcurrentSessionFilter requires two properties, sessionRegistry, which generally points to an instance of SessionRegistryImpl, and expiredUrl, which points to the page to display when a session has expired. A configuration using the namespace to create the FilterChainProxy and other default beans might look like this:

<http>
<custom-filter position="CONCURRENT_SESSION_FILTER" ref="concurrencyFilter" />
<custom-filter position="FORM_LOGIN_FILTER" ref="myAuthFilter" />

<session-management session-authentication-strategy-ref="sas"/>
</http>

<beans:bean id="concurrencyFilter"
class="org.springframework.security.web.session.ConcurrentSessionFilter">
<beans:property name="sessionRegistry" ref="sessionRegistry" />
<beans:property name="expiredUrl" value="/session-expired.htm" />
</beans:bean>

<beans:bean id="myAuthFilter" class=
"org.springframework.security.web.authentication.UsernamePasswordAuthenticationFilter">
<beans:property name="sessionAuthenticationStrategy" ref="sas" />
<beans:property name="authenticationManager" ref="authenticationManager" />
</beans:bean>

<beans:bean id="sas" class="org.springframework.security.web.authentication.session.CompositeSessionAuthenticationStrategy">
<beans:constructor-arg>
	<beans:list>
	  <beans:bean class="org.springframework.security.web.authentication.session.ConcurrentSessionControlAuthenticationStrategy">
		<beans:constructor-arg ref="sessionRegistry"/>
		<beans:property name="maximumSessions" value="1" />
		<beans:property name="exceptionIfMaximumExceeded" value="true" />
	  </beans:bean>
	  <beans:bean class="org.springframework.security.web.authentication.session.SessionFixationProtectionStrategy">
	  </beans:bean>
	  <beans:bean class="org.springframework.security.web.authentication.session.RegisterSessionAuthenticationStrategy">
		<beans:constructor-arg ref="sessionRegistry"/>
	  </beans:bean>
	</beans:list>
</beans:constructor-arg>
</beans:bean>

<beans:bean id="sessionRegistry"
	class="org.springframework.security.core.session.SessionRegistryImpl" />

Adding the listener to web.xml causes an ApplicationEvent to be published to the Spring ApplicationContext every time a HttpSession commences or terminates. This is critical, as it allows the SessionRegistryImpl to be notified when a session ends. Without it, a user will never be able to log back in again once they have exceeded their session allowance, even if they log out of another session or it times out.