code: def import_oauth2_credentials(filename=STORAGE_FILENAME):
      
      with open(filename, 'r') as storage_file:
          storage = safe_load(storage_file)
  
      # depending on OAuth 2.0 grant_type, these values may not exist
      client_secret = storage.get('client_secret')
      refresh_token = storage.get('refresh_token')
  
      credentials = {
          'access_token': storage['access_token'],
          'client_id': storage['client_id'],
          'client_secret': client_secret,
          'expires_in_seconds': storage['expires_in_seconds'],
          'grant_type': storage['grant_type'],
          'refresh_token': refresh_token,
          'scopes': storage['scopes'],
      }
  
      return credentials
docs: Import OAuth 2.0 session credentials from storage file.
      Parameters
          filename (str)
              Name of storage file.
      Returns
          credentials (dict)
              All your app credentials and information
              imported from the configuration file.