How to programatically set up/chain JAAS login realms as if loaded from a login.conf?

Question

I am trying to figure out how I can programatically set up several custom authentication realms and chain the authentication through them. I can't seem to be able to find what actually is parsing the typical login.conf file (in JAAS) and how I can basically achieve the same effect programatically.

Is the best way to do this to have sort of a proxy login module which checks what login modules exist, or is there a better way to do this?

Another way I can think of is to find what JAAS realms can be found via a ServiceLoader, confguration files, or something along those lines and then generate a login.conf and override the system property for this.

None of these look like the proper way to do it.

Could somebody recommend something else, maybe?

Many thanks for your help!