code: def _auth(self, username, password) :
          
          self.user_credentials = self.call('auth', {'username': username, 'password': password})
          
          if 'error' in self.user_credentials:
              raise T411Exception('Error while fetching authentication token: %s'\
                      % self.user_credentials['error'])
          # Create or update user file
          user_data = dumps({'uid': '%s' % self.user_credentials['uid'], 'token': '%s' % self.user_credentials['token']})
          with open(USER_CREDENTIALS_FILE, 'w') as user_cred_file:
              user_cred_file.write(user_data)
          return True
docs: Authentificate user and store token