code: def access_token():
      
      client = Client.query.filter_by(
          client_id=request.form.get('client_id')
      ).first()
  
      if not client:
          abort(404)
  
      if not client.is_confidential and \
              'client_credentials' == request.form.get('grant_type'):
          error = InvalidClientError()
          response = jsonify(dict(error.twotuples))
          response.status_code = error.status_code
          abort(response)
  
      # Return None or a dictionary. Dictionary will be merged with token
      # returned to the client requesting the access token.
      # Response is in application/json
      return None
docs: Token view handles exchange/refresh access tokens.