The correct link is http://www.eclipse.org/jetty/documentation/current/configuring-security-authentication.html for how to secure jetty.
There are multiple means of doing this documented there. My personal favorite is to use SSL client security.
Another option which might provide better integration with a secured Hortonworks cluster would be to use Knox to proxy the solr interface, and use Knox for authentication or single sign on.
The Knox Developers' Guide has more information on how to configure a proxy for non-default services such as the banana and solr web endpoints.