Thanks Daniel.
I gave that another try, and still get the same error you posted above:
09:03:55,149 TRACE org.jboss.modules (Remoting "1001467" task-2) Finding class com.mycompany.security.loginmodule.MagicLoginModule from Module "org.jboss.as.remoting:main" from local module loader @b4e29b (roots: /opt/jboss-as-7.1.1.Final/modules)
09:03:55,150 TRACE org.jboss.modules (Remoting "1001467" task-2) Class com.mycompany.security.loginmodule.MagicLoginModule not found from Module "org.jboss.as.remoting:main" from local module loader @b4e29b (roots: /opt/jboss-as-7.1.1.Final/modules)
Was there something else you needed to configure, or do I need to download a new build or something?