apache httpclient proxy authentication

To authenticate with a proxy server using Apache HttpClient, you can use the CredentialsProvider interface to supply the necessary authentication credentials. Here's an example that demonstrates how to use Basic Authentication with a proxy server:

import org.apache.http.HttpHost;
import org.apache.http.auth.AuthScope;
import org.apache.http.auth.UsernamePasswordCredentials;
import org.apache.http.client.CredentialsProvider;
import org.apache.http.impl.client.BasicCredentialsProvider;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;
import org.apache.http.impl.conn.DefaultProxyRoutePlanner;
import org.apache.http.util.EntityUtils;

public class HttpClientExample {
    public static void main(String[] args) throws Exception {
        HttpHost proxy = new HttpHost("proxy.example.com", 8080);
        DefaultProxyRoutePlanner routePlanner = new DefaultProxyRoutePlanner(proxy);

        String proxyUsername = "proxyuser";
        String proxyPassword = "proxypassword";
        CredentialsProvider credentialsProvider = new BasicCredentialsProvider();
        credentialsProvider.setCredentials(new AuthScope(proxy),
            new UsernamePasswordCredentials(proxyUsername, proxyPassword));

        CloseableHttpClient httpClient = HttpClients.custom()
            .setDefaultCredentialsProvider(credentialsProvider)
            .setRoutePlanner(routePlanner)
            .build();

        HttpGet httpGet = new HttpGet("http://www.example.com");
        String responseBody = EntityUtils.toString(httpClient.execute(httpGet).getEntity());
        System.out.println(responseBody);
    }
}

In this example, we first create an instance of HttpHost that represents the proxy server and configure it with the proxy host name and port number. We then create an instance of DefaultProxyRoutePlanner using the HttpHost object, and set it as the route planner for the CloseableHttpClient object using the setRoutePlanner() method. Next, we create an instance of CredentialsProvider and set it to use Basic Authentication with the proxy server. We then set the CredentialsProvider on the CloseableHttpClient object using the setDefaultCredentialsProvider() method. Finally, we execute an HTTP GET request using the CloseableHttpClient object, and extract the response body using the EntityUtils class.

Note that this example demonstrates how to use Basic Authentication with a single username and password. For more complex authentication scenarios, such as using different credentials for different proxy servers, you may need to use more advanced authentication techniques, such as Digest Authentication or NTLM Authentication. You can find more information about these techniques in the Apache HttpClient documentation.