Django password problems

I'm using a modelform for User like so:

class UserForm(forms.ModelForm):
    class Meta:
        model = User
        fields = ('username','password','email',)

but the password field shows up as a regular textfield, not a password input. How do I make sure it shows a password field?

I tried this:

class UserForm(forms.ModelForm):
    username = forms.CharField(max_length = 15, min_length = 6)
    password = forms.PasswordInput() 
    class Meta:
        model = User
        fields = ('username','password','email',)

but that doesn't work either.

I'm also trying to add a confirm password field like so, but this causes no fields to be displayed:

class UserForm(forms.ModelForm):
    username = forms.CharField(max_length = 15, min_length = 6)
    password = forms.PasswordInput()
    cpassword = forms.PasswordInput()

    def clean(self):
        if self.cleaned_data['cpassword']!=self.cleaned_data['password']:
            raise forms.ValidationError("Passwords don't match")

    class Meta:
        model = User
        fields = ('username','password','cpassword','email',)