title: Extract Keyfile JSON from saved connection of type "google_cloud_platform"
body: <p>I have saved a connection of type "google_cloud_platform" in Airflow as described here <a href="https://cloud.google.com/composer/docs/how-to/managing/connections" rel="nofollow noreferrer">https://cloud.google.com/composer/docs/how-to/managing/connections</a></p>
  
  <p>Now in my DAG, I need to extract from the saved connection the Keyfile JSON</p>
  
  <p>What is the correct hook to be used?</p>