“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

Such behaviour may occur if you did not add api user in admin panel (in your case Documents panel I guess), for instance in google analytics you have to add new user where email address is the same which you got from api (provided by the Google API Service Account, after creating private key). In analytics it looks like this: