Nathan, JAAS configuration is wide used industry standard (http://docs.oracle.com/javase/1.5.0/docs/guide/security/jaas/tutorials/LoginConfigFile.html), and we should avoid invent a new wheel here. For example, ZK is taking a similar approach, see http://hbase.apache.org/book/zk.sasl.auth.html.
The standard JAAS configuration also enables us to use JDK lib for authentication (javax.security.auth.*).