django allauth get extra data in request.user

class SignupForm(forms.Form):
    first_name = forms.CharField(max_length=30, label='Voornaam')
    last_name = forms.CharField(max_length=30, label='Achternaam')

    def signup(self, request, user):
        user.first_name = self.cleaned_data['first_name']
        user.last_name = self.cleaned_data['last_name']
        user.save()