code: def auth(self, username, password):
          
          if username not in self.users:
              return False
          elif self.users[username][self.pwd_attr] == password:
              return True
          return False
docs: Check authentication against the backend
  
          :param username: 'key' attribute of the user
          :type username: string
          :param password: password of the user
          :type password: string
          :rtype: boolean (True is authentication success, False otherwise)