code: def optionsFromEnvironment(defaults=None):
      
      options = defaults or {}
      credentials = options.get('credentials', {})
  
      rootUrl = os.environ.get('TASKCLUSTER_ROOT_URL')
      if rootUrl:
          options['rootUrl'] = rootUrl
  
      clientId = os.environ.get('TASKCLUSTER_CLIENT_ID')
      if clientId:
          credentials['clientId'] = clientId
  
      accessToken = os.environ.get('TASKCLUSTER_ACCESS_TOKEN')
      if accessToken:
          credentials['accessToken'] = accessToken
  
      certificate = os.environ.get('TASKCLUSTER_CERTIFICATE')
      if certificate:
          credentials['certificate'] = certificate
  
      if credentials:
          options['credentials'] = credentials
  
      return options
docs: Fetch root URL and credentials from the standard TASKCLUSTER_…
      environment variables and return them in a format suitable for passing to a
      client constructor.