SEAM 2.1.2 introduced the "add-identity-management" keyword, which can generate a fully functional SEAM JpaIdentityManagement powered security management system.

Here is a blog post explaining what it is: http://blog.hibernate.org/10904.lace
Here is the seam-gen documentation for this feature: http://seamframework.org/Documentation/AddIdentityManagementToASeamgenProject

Would also be nice to have an example project with this stuff already set up to play around with.