Currently, you must manually map principals to roles in the security component of a deployment descriptor. In the common case where group names match role names, this seems like unnecessary overhead.
Alan and I talked and our plan is to make the role-mapping parts of the security elements look something like this:
The automatic-role-mapping is the new bit. If you specify that element empty, it would map every principal type the security realm considers to be a group to roles. For example, if you configure the seucrity realm to consider the principal class "foo.GroupPrincipal" as a role, and use an empty automatic-role-mapping element, that's what you'd get. You can also manually specify one or more principal classes that should be automatically mapped to roles. In any of these cases, the "automatic" mapping is done based on the role name and group name matching.
If you specify automatic mapping and individual role mapping, then the user just needs to qualify for the role based on either one or the other (not both). So you could use a manual role mapping to add eligible users on top of the automatic role mapping, but not to subtract users from the automatic role mapping.