“Login Required” 401 Unauthorized message when calling the v3 Google Calendar API using a Service Account via OAuth 2.0

Question

First, let me explain what I am trying to do, as this is a two part question.

I am building a JAX-RS service that internally authenticates with a Google account via

Answer 1

As for the 401, it seems some oddity with Google's API. I find the first time I run my app in a while, and then at seemingly random intervals hours spread apart, I always get a 401. On the second or third round it actually logs in.

The behavior is even accounted for in Google's Task API sample code here.

Notice this code:

void onRequestCompleted() {
received401 = false;
}

void handleGoogleException(IOException e) {
if (e instanceof GoogleJsonResponseException) {
  GoogleJsonResponseException exception = (GoogleJsonResponseException) e;
  if (exception.getStatusCode() == 401 && !received401) {
    received401 = true;
    accountManager.invalidateAuthToken(credential.getAccessToken());
    credential.setAccessToken(null);
    SharedPreferences.Editor editor2 = settings.edit();
    editor2.remove(PREF_AUTH_TOKEN);
    editor2.commit();
    gotAccount();
    return;
  }
}
Log.e(TAG, e.getMessage(), e);

}

In Google's own code sample they have made provision for a first time 401. It might be some special security issue that needs to be handled in code.