title: How to use Apache Beam Direct runner to authenticate with GOOGLE_APPLICATION_CREDENTIALS
body: <p>How to use Apache Beam Direct runner to authenticate with GOOGLE_APPLICATION_CREDENTIALS?
  I don't want to authenticate using gcloud account. I have a service account(json) which I set as System variable. How do I have Apache Beam program(running as DirectRunner) authenticate using that GOOGLE_APPLICATION_CREDENTIALS?</p>
  
  <p>My usecase would be access GCP Pub/Sub resources in the Apache beam program, so need to authenticate</p>