I am trying to connect to solr using solrj. My solr instance runs in jetty and is protected with basic authentication. I found these links that contain relevant information.
According to the Solr Security - SolrJ section on Solr Wiki you should be able to do the following:
public static void main(String[] args) throws SolrServerException, IOException {
HttpSolrServer server = new HttpSolrServer("http://localhost:8983/solr/");
HttpClientUtil.setBasicAuth(server.getHttpClient(), USERNAME, PASSWORD);
SolrInputDocument document = new SolrInputDocument();
document.addField("id",123213);
server.add(document);
server.commit();
}