I'm currently testing django 1.5 and a custom User model, but I've some problems. I've created a User class in my account app, which looks like:

class User(AbstractBaseUser):
    email = models.EmailField()
    activation_key = models.CharField(max_length=255)
    is_active = models.BooleanField(default=False)
    is_admin = models.BooleanField(default=False)

    USERNAME_FIELD = 'email'

I can correctly register a user, who is stored in my account_user table. Now, how can I log in? I've tried with:

def login(request):
    form = AuthenticationForm()
    if request.method == 'POST':
        form = AuthenticationForm(request.POST)
        email =  request.POST['username']
        password = request.POST['password'] 
        user = authenticate(username=email, password=password)
        if user is not None:
            if user.is_active:
                login(user)
            else:
                message = 'disabled account, check validation email'
                return render(
                        request, 
                        'account-login-failed.html', 
                        {'message': message}
                )
    return render(request, 'account-login.html', {'form': form})

I can correctly register a new User

My forms.py which contains my register form

class RegisterForm(forms.ModelForm):
    """ a form to create user"""
    password = forms.CharField(
            label="Password",
            widget=forms.PasswordInput()
    )
    password_confirm = forms.CharField(
            label="Password Repeat",
            widget=forms.PasswordInput()
    )
    class Meta:
        model = User
        exclude = ('last_login', 'activation_key')

    def clean_password_confirm(self):
        password = self.cleaned_data.get("password")
        password_confirm = self.cleaned_data.get("password_confirm")
        if password and password_confirm and password != password_confirm:
            raise forms.ValidationError("Password don't math")
        return password_confirm

    def clean_email(self):
        if User.objects.filter(email__iexact=self.cleaned_data.get("email")):
            raise forms.ValidationError("email already exists")
        return self.cleaned_data['email']

    def save(self):
        user = super(RegisterForm, self).save(commit=False)
        user.password = self.cleaned_data['password']
        user.activation_key = generate_sha1(user.email)
        user.save()

        return user

My question is: Why does authenticate give me None? I know I'm trying to authenticate() with an email as username but is that not one of the reasons to use a custom User model?