带有gae服务帐户的googleads api

Question

我正在尝试使用GoogleCredentials.get_application_default（）在GAE中使用服务帐户凭据访问Google Ads API。

继续收到OAUTH_TOKEN_INVALID错误。

我的代码：

service_cred = GoogleCredentials.get_application_default()
service_ads_auth = GoogleServiceAccountClient(service_cred)
service_customer_service = service_ads_client.GetService('CustomerService')
print service_customer_service.getCustomers()

class GoogleServiceAccountClient(oauth2.GoogleOAuth2Client):
    def __init__(self, service_credentials):
        """Initializes a GoogleServiceAccountClient."""
        self.creds = service_credentials
        def CreateHttpHeader(self):
    self.creds.get_access_token()
        oauth2_header = {}
        self.creds.apply(oauth2_header)
        return oauth2_header

我不知道为什么令牌无效？