I implemented a Liferay portlet. This portlet is an iframe that loads Alfresco Explorer, passing a parameter (ticket) to authenticate the user. The ticket was previously achieved by code and is passed to the URL of Alfresco Explorer.
I'm not surprised anybody answers to your question, Since even it is a valid one, The new authentication philosophy proposed by alfresco implementation, is to publish the /share.war app as a portlet, and activate external authentication filter.