...and here's how I set up the security realm:
sudo -u www-data \
$GLASSFISH_HOME/bin/asadmin create-auth-realm \
--classname com.sun.enterprise.security.auth.realm.jdbc.JDBCRealm \
--property jaas-context=jdbcRealm:datasource-jndi=jdbc/fpdb:user-table=users:user-name-column=username:password-column=password:digest-algorithm=md5:group-table=users_roles:group-name-column=rolename fp-realm
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