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.