获得403 - 禁止使用Google服务帐户

我正在尝试获取Google服务帐户的访问令牌.以下是我的代码 -

String SERVICE_ACCOUNT_EMAIL = "edited@developer.gserviceaccount.com";
List scope = new ArrayList();
scope.add("https://www.googleapis.com/auth/admin.directory.user");
String keyFile = "C:\\edited-privatekey.p12";
HttpTransport HTTP_TRANSPORT = new NetHttpTransport();
JsonFactory JSON_FACTORY = new JacksonFactory();
GoogleCredential credential = new GoogleCredential.Builder()
.setTransport(HTTP_TRANSPORT)
.setJsonFactory(JSON_FACTORY)
.setServiceAccountId(SERVICE_ACCOUNT_EMAIL)
.setServiceAccountScopes(scope)
.setServiceAccountPrivateKeyFromP12File(new java.io.File(keyFile))
.build();

credential.refreshToken();
String accessTokens = credential.getAccessToken();

虽然代码工作正常但我确实获得了访问令牌,但当我尝试使用Google Directory API"GET"Google Apps用户时,我会收到403 - 禁止响应代码.有人可以帮忙吗？
我知道GET用户的代码是正确的,因为它适用于Google Apps管理员生成的访问令牌.