在 Google 服务帐户中获取访问令牌为 Null

Question

我正在使用 Google 服务帐户使用以下代码从服务端获取访问令牌。但我得到的访问令牌为空。相同的返回令牌将用于在客户端为相同的 userEmailId 打开 Google 文件选择器。请建议我在代码中做错了什么。

private static final List SCOPE = Arrays.asList("https://www.googleapis.com/auth/drive");

public String getAccessToken(String SERVICE_ACCOUNT_EMAIL, String SERVICE_ACCOUNT_PKCS12_FILE_PATH,String userEmailId){
                try {
                    HttpTransport httpTransport = new NetHttpTransport();
                    JsonFactory jsonFactory = new JacksonFactory();
                    GoogleCredential credential = new GoogleCredential.Builder()
                                                    .setTransport(httpTransport)
                                                    .setJsonFactory(jsonFactory)
                                                    .setServiceAccountId(SERVICE_ACCOUNT_EMAIL)
                                                    .setServiceAccountScopes(SCOPE)
                                                    .setServiceAccountUser(userEmailId)
                                                    .setServiceAccountPrivateKeyFromP12File(new java.io.File(SERVICE_ACCOUNT_PKCS12_FILE_PATH))
                                                    .build();

                    credential.getRefreshToken();
                    return credential.getAccessToken();
                } catch (Exception e) {
                    // TODO: handle exception
                    log.severe("Error while getting Drive  credentilas. 5.0"+ e.getMessage());
                    return null;
                }
            }

Answer 1

对于那些使用 Firebase Admin SDK（即 GoogleCredentials 类）的人来说，这就可以了。

GoogleCredentials credentials = GoogleCredentials.fromStream(serviceAccount).createScoped(Arrays.asList("https://www.googleapis.com/auth/firebase.messaging"));
credentials.refresh();
credentials.getAccessToken();