username = forms.CharField(max_length=150) password = forms.CharField(widget=forms.PasswordInput)
and then a view to instantiate form with request.POST (if request.POST) like:
form = LoginForm(request.POST)
and then if form.is_valid() you can clean data using
username = form.cleaned_data['username']
and the same for password.
Then:
user = authenticate(request, username=username, password=password)
and then check if user is not None then login(request, user)
Note that login and authenticate come from django.contrib.auth import authenticate, login
Hope that helps.