google OAuth2获取服务帐户的访问令牌：连接超时

Question

我正在使用Google OAuth2代表服务帐户与Google DialogFlow API进行服务器到服务器的交互。 但是当尝试生成访问令牌（credentials.refreshIfExpired（））时出现错误：

java.io.IOException: Error getting access token for service account: connect timed out

此处是代码：

    GoogleCredentials credentials = GoogleCredentials.fromStream(new FileInputStream(System.getenv("GOOGLE_APPLICATION_CREDENTIALS")));

    if (credentials.createScopedRequired()) {
        credentials = credentials.createScoped(Collections.singletonList("https://www.googleapis.com/auth/dialogflow"));
    }

    credentials.refreshIfExpired();
    AccessToken token = credentials.getAccessToken();

    System.out.println(token.getTokenValue());

我试图通过多种方式找到解决方案，有人说这可能导致我的服务器时间与Google时间之间的同步。

然后我在格林尼治标准时间设置默认timeZone

@SpringBootApplication
public class DialogFlowDemoApplication {

    @PostConstruct
    public void init(){
        TimeZone.setDefault(TimeZone.getTimeZone("GMT"));
        System.out.println("Spring boot application running in GMT timezone :"+new Date());
    }

    public static void main(String[] args) {

        SpringApplication.run(DialogFlowDemoApplication.class, args);

    }
}

但这没有帮助，这真的让我发疯。

我的依赖关系如下：

<!--start google dependencies-->
<dependency>
    <groupId>com.google.cloud</groupId>
    <artifactId>google-cloud-dialogflow</artifactId>
    <version>0.108.0-alpha</version>
</dependency>

<dependency>
    <groupId>com.google.oauth-client</groupId>
    <artifactId>google-oauth-client</artifactId>
    <version>1.30.1</version>
</dependency>

<dependency>
    <groupId>com.google.cloud</groupId>
    <artifactId>google-cloud-storage</artifactId>
    <version>1.90.0</version>
</dependency>

<dependency>
    <groupId>com.google.api-client</groupId>
    <artifactId>google-api-client</artifactId>
    <version>1.30.4</version>
</dependency>
<!--end of google dependencies--> 

请帮助，谢谢！