SAML authenticated users don't appear in Spring Security's SessionRegistry

Our application used to have only one possibility to log in: username and password. Once a new user logged into the application, their session would appear in Spring Security's SessionRegistry.

Now I'm implementing SAML support with the help of Spring SAML. I oriented the setup heavily towards the sample application's configuration. It all works fine. However I noticed that users that log in via SAML don't get their session added to the SessionRegistry.

The usual context file for form based authentication contains the following:

<session-management 
  invalid-session-url="/login"
  session-fixation-protection="newSession"
  session-authentication-error-url="/login?invalid_session=1">

  <concurrency-control
    max-sessions="1"
    error-if-maximum-exceeded="false"
    session-registry-alias="springSessionRegistry"/>

</session-management>

In my http element for the SAML configuration I added the same. This created a new SessionRegistry but it did not contain anything. I also tried

<concurrency-control session-registry-ref="springSessionRegistry"/>

but this did not contain any SAML authenticated sessions either.

So how can I access SAML sessions?