@Field
    public void setAuthScheme(String authScheme) {
        httpClientFactory.setAuthScheme(authScheme);
    }
Specify the field in the first Metadata that should be
used as the id field for the document.

@param idField
tika-pipes/tika-emitters/tika-emitter-solr/src/main/java/org/apache/tika/pipes/emitter/solr/SolrEmitter.java