title: Dataflow access to pubsub access tokens
body: <p>When running my apache beam / google dataflow pipeline locally, the python SDK seems to request a new auth token on each input into the streaming pipeline - is this normal?</p>
  
  <pre><code>INFO:oauth2client.transport:Attempting refresh to obtain initial access_token
  INFO:oauth2client.client:Refreshing access_token
  </code></pre>