[[_limit-authentication-sessions]]
=== Limit Authentication Sessions

When a login page is opened for the first time in a web browser, {project_name} creates an object called authentication session that stores some useful information about the request.
Whenever a new login page is opened from a different tab in the same browser, {project_name} creates a new record called authentication sub-session that is stored within the authentication session.
Authentication requests can come from any type of clients such as the Admin CLI. In that case, a new authentication session is also created with one authentication sub-session.
Please note that authentication sessions can be created also in other ways than using a browser flow. The text below is applicable regardless of the source flow.   

NOTE: This section describes deployments that use the {jdgserver_name} provider for authentication sessions.

Authentication session is internally stored as `RootAuthenticationSessionEntity`. Each `RootAuthenticationSessionEntity` can have multiple authentication sub-sessions stored within the
`RootAuthenticationSessionEntity` as a collection of `AuthenticationSessionEntity` objects. {project_name} stores authentication sessions in a dedicated {jdgserver_name} cache.
The number of `AuthenticationSessionEntity` per `RootAuthenticationSessionEntity` contributes to the size of each cache entry. Total memory footprint of authentication session cache is determined by 
the number of stored `RootAuthenticationSessionEntity` and by the number of `AuthenticationSessionEntity` within each `RootAuthenticationSessionEntity`.

The number of maintained `RootAuthenticationSessionEntity` objects corresponds to the number of unfinished login flows from the browser. To keep the number of `RootAuthenticationSessionEntity`
under control, using an advanced firewall control to limit ingress network traffic is recommended.

 
Higher memory usage may occur for deployments where there are many active `RootAuthenticationSessionEntity` with a lot of `AuthenticationSessionEntity`.
If the load balancer does not support or is not configured for link:{installguide_stickysessions_link}[session stickiness], the load over network in a cluster can
increase significantly. The reason for this load is that each request that lands on a node that does not own the appropriate authentication session needs to retrieve
and update the authentication session record in the owner node which involves a separate network transmission for both the retrieval and the storage.
  
The maximum number of `AuthenticationSessionEntity` per `RootAuthenticationSessionEntity` can be configured in `authenticationSessions` SPI by setting property `authSessionsLimit`. The default value is set to 300 `AuthenticationSessionEntity` per a `RootAuthenticationSessionEntity`. When this limit is reached, the oldest authentication sub-session will be removed after a new authentication session request.

The following example shows how to limit the number of active `AuthenticationSessionEntity` per a `RootAuthenticationSessionEntity` to 100.


[source,xml]
----     
<subsystem xmlns="urn:jboss:domain:keycloak-server:1.1">
    ...
    <spi name="authenticationSessions">
        <default-provider>infinispan</default-provider>
        <provider name="infinispan" enabled="true">
            <properties>
                <property name="authSessionsLimit" value="100"/>
            </properties>
        </provider>
    </spi>
    ...
</subsystem>
----

Equivalent configuration using CLI commands:

[source,bash]
----
/subsystem=keycloak-server/spi=authenticationSessions:add(default-provider=infinispan)
/subsystem=keycloak-server/spi=authenticationSessions/provider=infinispan:add(properties={authSessionsLimit => "100"},enabled=true)
----