Accessing J2EE container authentication information

[John Smith]

We planning to use the standard j2ee authentication mechanisms basic/form
etc. We also want to be able to configure individual permissions for users
within our app. We would like to have a screen where an admin can assign
permissions. The questions is given the authentication is done by the
container is it possible from our app within the container to find out what
Realm is being used. I can find out the method (basic/form etc) by parsing
the web.xml, tomcat stores the relam information in the server.xml, is the
same for other web servers? Is there an API for getting a list of valid
users from the container?

Thanks

Jon