<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def validate_authentication(self, username, password, handler):
 """authenticate user with password """

        user = authenticate(
            **{self.username_field: username, 'password': password}
        )
        account = self.get_account(username)
        if not (user and account):
            raise AuthenticationFailed("Authentication failed.")