官方文档地址：Basic authentication

    可以通过提供HttpClientConfigCallback来配置基本身份验证，同时通过其构建器构建RestClient。该接口有一个方法，该方法接收org.apache.http.impl.nio.client.HttpAsyncClientBuilder的实例作为参数，并具有相同的返回类型。可以修改并返回 http 客户端构建器。在下面的示例中，我们设置了一个需要基本身份验证的默认凭据提供程序。

    1. final CredentialsProvider credentialsProvider =
    2.     new BasicCredentialsProvider();
    3. credentialsProvider.setCredentials(AuthScope.ANY,
    4.     new UsernamePasswordCredentials("user", "test-user-password"));
    6. RestClientBuilder builder = RestClient.builder(
    7.     new HttpHost("localhost", 9200))
    8.     .setHttpClientConfigCallback(new HttpClientConfigCallback() {
    9.         @Override
    10.         public HttpAsyncClientBuilder customizeHttpClient(
    11.                 HttpAsyncClientBuilder httpClientBuilder) {
    12.             return httpClientBuilder
    13.                 .setDefaultCredentialsProvider(credentialsProvider);
    14.         }
    15.     });

    可以禁用抢占式身份验证，这意味着每个请求都将在没有授权头的情况下发送，以查看是否被接受，并且在收到 HTTP 401 响应时，它将重新发送与基本身份验证头完全相同的请求。如果你想这样做，那么你可以通过HttpAsyncClientBuilder来禁用它：

    1. final CredentialsProvider credentialsProvider =
    2.     new BasicCredentialsProvider();
    3. credentialsProvider.setCredentials(AuthScope.ANY,
    4.     new UsernamePasswordCredentials("user", "test-user-password"));
    6. RestClientBuilder builder = RestClient.builder(
    7.     new HttpHost("localhost", 9200))
    8.     .setHttpClientConfigCallback(new HttpClientConfigCallback() {
    9.         @Override
    10.         public HttpAsyncClientBuilder customizeHttpClient(
    11.                 HttpAsyncClientBuilder httpClientBuilder) {
    12.             //禁用抢占式身份验证
    13.             httpClientBuilder.disableAuthCaching(); 
    14.             return httpClientBuilder
    15.                 .setDefaultCredentialsProvider(credentialsProvider);
    16.         }
    17.     });