[keycloak-user] Logout from IDP with Spring Keycloak adaptor

I have a Keycloak Security Adaptor setup with a logout URL "/sso/logout". The user logins in using to my application using an IDP, and then logs out by POSTing to the /sso/logout the - they are redirected to the login page. However when attempted to login again, the user doesn't need to reauthenticate. It seems Spring doesn't logout from the IDP. Is there a simple way to get Spring to logout from the IDP? Should I change the logout URL?