在Apache HttpClient中，Digest Authentication（摘要认证）协议在处理Challenge时，不会自动转发"opaque"值。但可以通过自定义的AuthSchemeFactory来解决这个问题。

以下是一个示例代码，演示如何自定义AuthSchemeFactory来处理Digest Authentication的Challenge，并在请求中添加"opaque"值：

import org.apache.http.HttpHost;
import org.apache.http.HttpResponse;
import org.apache.http.auth.AuthScheme;
import org.apache.http.auth.AuthSchemeFactory;
import org.apache.http.auth.AuthScope;
import org.apache.http.auth.UsernamePasswordCredentials;
import org.apache.http.client.AuthCache;
import org.apache.http.client.AuthCacheValue;
import org.apache.http.client.CredentialsProvider;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.client.protocol.HttpClientContext;
import org.apache.http.impl.auth.DigestScheme;
import org.apache.http.impl.auth.DigestSchemeFactory;
import org.apache.http.impl.client.BasicAuthCache;
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.protocol.HttpContext;

public class HttpClientDigestAuthExample {
    public static void main(String[] args) throws Exception {
        CloseableHttpClient httpClient = HttpClients.custom()
                .setDefaultAuthSchemeRegistry(
                        HttpClientContext.getDefaultAuthSchemeRegistry())
                .setDefaultCredentialsProvider(
                        new BasicCredentialsProvider())
                .build();

        AuthSchemeFactory digestAuthFactory = new DigestSchemeFactory() {
            @Override
            public AuthScheme create(HttpContext context) {
                return new DigestScheme() {
                    @Override
                    public void processChallenge(
                            final Header header) throws MalformedChallengeException {
                        super.processChallenge(header);
                        String opaque = getParameter("opaque");
                        if (opaque != null) {
                            setParameter("opaque", opaque);
                        }
                    }
                };
            }
        };

        AuthSchemeFactory.register("Digest", digestAuthFactory);

        HttpHost targetHost = new HttpHost("example.com", 80, "http");
        CredentialsProvider credsProvider = new BasicCredentialsProvider();
        credsProvider.setCredentials(
                new AuthScope(targetHost.getHostName(), targetHost.getPort()),
                new UsernamePasswordCredentials("username", "password"));

        AuthCache authCache = new BasicAuthCache();
        authCache.put(targetHost, new AuthCacheValue(
                new DigestScheme()));
        HttpClientContext context = HttpClientContext.create();
        context.setCredentialsProvider(credsProvider);
        context.setAuthCache(authCache);

        HttpGet httpGet = new HttpGet("/");
        HttpResponse response = httpClient.execute(targetHost, httpGet, context);
        // 处理响应
    }
}

在上述示例中，我们自定义了一个AuthSchemeFactory实现，并在其中重写了DigestScheme的processChallenge方法。在该方法中，我们首先调用父类的processChallenge方法处理Challenge，然后获取"opaque"值，并将其设置回DigestScheme中。

最后，我们将自定义的AuthSchemeFactory注册到HttpClient中，以便在进行Digest Authentication时使用。