Django用户名允许非ascii字符

Question

Django用户名是不允许非ascii，有没有办法覆盖模型中的用户名，然后它会接受非ascii字符？

class RegiForm(ModelForm):
username = forms.CharField()
password=forms.CharField(label=(u'password'), widget=forms.PasswordInput(render_value=False))
password2=forms.CharField(label=(u'password2'), widget=forms.PasswordInput(render_value=False))

def clean_username(self):