Google Cloud Datastore . net客户端API拒绝403权限

使用新的Google Cloud Datastore v1beta客户端库，我得到

{
 "error": {
  "errors": [
   {
    "domain": "global",
    "reason": "PERMISSION_DENIED",
    "message": "Unauthorized."
   }
  ],
  "code": 403,
  "message": "Unauthorized."
 }
}

的任何请求。我创建了一个应用引擎应用，添加了云数据存储API，配置了一个服务帐户，我正在使用它来验证我的请求。

[TestMethod]
public void BasicBlindWrite()
{
    var service = new DatastoreService(new BaseClientService.Initializer() { Authenticator = CreateAuthenticator() });
    var request = new GoogleData.BlindWriteRequest();
    var entity = new GoogleData.Entity();
    entity.Key = new GoogleData.Key();
    entity.Key.Path = new List<KeyPathElement>();
    entity.Key.Path.Add(new GoogleData.KeyPathElement { Kind = "Consumer", Name = "Consumer-1" });
    var firstName = new GoogleData.Property();
    firstName.Values = new List<GoogleData.Value>();
    firstName.Values.Add(new GoogleData.Value { StringValue = "Samuel"});
    entity.Properties = new GoogleData.Entity.PropertiesData();
    entity.Properties.Add("FirstName", firstName);
    request.Mutation = new GoogleData.Mutation();
    request.Mutation.Upsert = new List<GoogleData.Entity>();
    request.Mutation.Upsert.Add(entity);
    var response = service.Datasets.BlindWrite(request, "my-appengine-project-id").Fetch();
}
private OAuth2Authenticator<AssertionFlowClient> CreateAuthenticator()
{
    var certificate = new X509Certificate2(TestClientCredentials.ClientCertificateFilePath, "notasecret",
        X509KeyStorageFlags.Exportable);
    var provider = new AssertionFlowClient(GoogleAuthenticationServer.Description, certificate)
    {
        ServiceAccountId = TestClientCredentials.CertificateEmailAddress,
        Scope = "https://www.googleapis.com/auth/userinfo.email https://www.googleapis.com/auth/datastore"
    };
    var authenticator = new OAuth2Authenticator<AssertionFlowClient>(provider, AssertionFlowClient.GetState);
    return authenticator;
}

如果我使用web API控制台，它工作。

** UPDATE **

下面是我创建服务帐户的方法:

1. 创建AppEngine应用程序。
2. 导航到Google api控制台。
3. 为AppEngine应用程序启用Google云数据存储API。
4. 点击"创建OAuth 2.0客户端ID…"
5. 给它一个假名字
6. 选择"服务帐户"作为申请类型。
7. 点击"创建客户端ID"。
8. 点击"下载私钥"(位置表示为TestClientCredentials)。ClientCertificateFilePath(代码如下)。