Firstly, thanx for help and interest.
Unfortunately I don't find the solution in the link you passed me. Let's anaylize this:
This relates to how to register additional provider in the existent Authentication manager.
describes hot to use existent authenticationManager created by namespace within a completely new filter.
<bean id="casProcessingFilter" class="org.springframework.security.ui.cas.CasProcessingFilter">
<property name="authenticationManager" ref="authenticationManager"/>
What I would like is to use personalized authenticationManager within existent filter or , what would be better, to replace default namespace authenticationManager with my own.
One again, thanx for the reply and sorry for being so blunt. For sure it's written there but I just don't get it. I would be grateful for any explanation.