title: Postman - JWT authentication using key file
body: <p>I am trying to use Postman to test API developed on Google Cloud Platform: App Engine behind an API endpoint.<br>
  I have the key file in the JSON format:</p>
  
  <pre><code>{
    "type": "service_account",
    "project_id": "[[my_project_name]]",
    "private_key_id": "[[private_key_id]]",
    "private_key": "-----BEGIN PRIVATE KEY-----\n[[private_key]]\n-----END PRIVATE KEY-----\n",
    "client_email": "[[service_account_email]]",
    "client_id": "",
    "auth_uri": "https://accounts.google.com/o/oauth2/auth",
    "token_uri": "https://oauth2.googleapis.com/token",
    "auth_provider_x509_cert_url": "https://www.googleapis.com/oauth2/v1/certs",
    "client_x509_cert_url": "https://www.googleapis.com/robot/v1/metadata/x509/[[service_account_email]]"
  }
  </code></pre>
  
  <p>And I am able to retrieve access token using python code:</p>
  
  <pre><code>import time
  import google.auth.crypt
  import google.auth.jwt
  
  sa_keyfile='[[path_to_the_api_key_file]]'
  sa_email='[[service_account_email]]'
  audience='[[my_api_url]]'
  expiry_length=3600
  now = int(time.time())
  payload = {
      'iat': now,
      "exp": now + expiry_length,
      'iss': sa_email,
      'aud':  audience,
      'sub': sa_email,
      'email': sa_email
  }
  
  signer = google.auth.crypt.RSASigner.from_service_account_file(sa_keyfile)
  jwt = google.auth.jwt.encode(signer, payload)
  
  print(jwt)
  </code></pre>
  
  <p>If I setup in Postman <code>OAuth 2.0</code> as authentication method and paste obtained JWT as <code>Access Token</code> then request is working just fine.  </p>
  
  <p>I would like to move whole JWT token operation into the Postman, without need to invoke Python code in advance. I tried to use <code>Get New Access Token</code> from Postman, but neither option supports JSON key file.<br>
  Is it possible to get JWT token from JSON key file using Postman only?</p>