Hi,
you're right, most of the documentation on user auth is in the API of the
MetadataProvider interface.
other than that you can find some informations in the FAQ (see
http://www.lightstreamer.com/vb/faq.php?faq=server_side#faq_metadata_adapterand
http://www.lightstreamer.com/vb/faq.php?faq=server_side#faq_notifyuser ) and in the General Concepts.pdf file section 4.1 (you can find that file on lightstreamer distribution under the DOCS-SDKs folder).
There are no examples available at the moment.
HTH