not sure if this is what you need, but did you consider using the 'UnauthenticatedPrincipal' ?
this way your struts tags will keep working and this principal is considered an an identity that has not been authenticated (logged in)
consider the following snippet from login-conf.xml, and see how the unauthenticated principal is named:
<application-policy name = "jbossmq">
<login-module code = "org.jboss.mq.sm.file.DynamicLoginModule"
flag = "required">
<module-option name = "unauthenticatedIdentity">guest</module-option>
<module-option name = "sm.objectname">jboss.mq:service=StateManager</module-option>
hope this helps