在clean函数中，如何在验证时获取对象？

from django import forms

class MyForm(forms.Form):
    username = forms.CharField(max_length=100)
    password = forms.CharField(widget=forms.PasswordInput)

    def clean(self):
        cleaned_data = super().clean()
        username = cleaned_data.get('username')
        password = cleaned_data.get('password')

        # 对获取的对象进行进一步的验证或处理
        if username and password:
            # 验证用户名和密码是否匹配
            if not authenticate(username=username, password=password):
                raise forms.ValidationError("用户名或密码不正确")

        return cleaned_data