Django表单无效，无法弄清原因

Question

我只是在Django中创建了一个注册表单，由于某些原因我无法解密，因此该表单无效。我添加了一个字段，用户可以在其中插入注册令牌，以防万一。

表格：

class SignupForm(UserCreationForm):     
    token = forms.CharField()
    class Meta:
        model = User
        fields = ('username', 'password')

模板：

<form action="/register/" method="post">
    {% csrf_token %}
    <label>Username:</label>{{ form.username }}<br>
    <label>Password:</label>{{ form.password }}<br>
    <label>Token:{{ form.token }}<br>
<button type="submit">Signup</button>
</form>

查看：

def signup(request):
    if request.method == 'GET':
        form = SignupForm()
        return render(request, 'signup.html',{'form':form})
    if request.method == 'POST' and  request.user.is_authenticated == False:
        form = SignupForm(request.POST)
        if form.is_valid(): #this is where it seems to be stuck
            user = form.save(commit=False)
            username = form.cleaned_data('username')
            password = form.cleaned_data('password')
            token = form.cleaned_data('token')
            if SignupToken.objects.filter(token = token).exists():
                user.save()
                db_token = RegistrationToken.objects.filter(token = token)
                db_token.delete()
                sign_in_user = authenticate(request, username, password)
                if sign_in_user is not None:
                    login(request, sign_in_user)
                    return redirect('home')
        else:
            message = 'Something went wrong.'
            return render(request, 'signup.html', {'message':message})