How to automatically login a user after registration in django

The accepted answer doesn't seem to work with Django 4.0 (for me, at least), or alternatively it doesn't work with custom user models that have custom user managers.

This is how I solved the issue (adapted from https://stackoverflow.com/a/31491942 and https://stackoverflow.com/a/68515276):

from django.views.generic import CreateView
from django.urls import reverse_lazy
from django.contrib.auth import authenticate, login
from your.custom.user.models import User

class SignUpView(CreateView):
    model = User
    fields = ["username", "email", "password"]
    success_url = reverse_lazy("success_url_name") # change this with your own URL

    def form_valid(self, form):
        # create the user object
        user = form.save(commit=False)
        # set password manually
        # as otherwise the User will be saved with unhashed password
        user.set_password(form.cleaned_data.get("password"))
        # save your User object to the database
        user.save()
        # get email and password
        email = form.cleaned_data.get("email")
        password = form.cleaned_data.get("password")
        # authenticate your user with unhashed password, because `authenticate` hashes it again
        authenticated_user = authenticate(email=email, password=password)
        # log in
        login(self.request, authenticated_user)
        return redirect(self.success_url)

You need to manually set the password, so that the database contains the hashed password. Without that, your unhashed password will be saved to the database, which will prevent you from logging in afterwards, as authentication involves hashing the password and checking that against the database.

for class based views here was the code that worked for me (originally Django 1.7, updated for 2.1)

from django.contrib.auth import authenticate, login
from django.contrib.auth.forms import UserCreationForm
from django.http import HttpResponseRedirect
from django.views.generic import FormView

class SignUp(FormView):
    template_name = 'signup.html'
    form_class = UserCreateForm
    success_url='/account'

    def form_valid(self, form):
        #save the new user first
        form.save()
        #get the username and password
        username = self.request.POST['username']
        password = self.request.POST['password1']
        #authenticate user then login
        user = authenticate(username=username, password=password)
        login(self.request, user)
        return HttpResponseRedirect(self.get_success_url)

You can subclass Django's UserCreationForm and override it's save method to log them in when commit=True.

forms.py

from django.contrib.auth.forms import UserCreationForm
from django.contrib.auth import login

class CustomUserCreationForm(UserCreationForm):
    """
    A ModelForm for creating a User and logging 
    them in after commiting a save of the form.
    """

    def __init__(self, request, *args, **kwargs):
        super().__init__(*args, **kwargs)
        self.request = request

    class Meta(UserCreationForm.Meta):
        pass

    def save(self, commit=True):
        user = super().save(commit=commit)
        if commit:
            auth_user = authenticate(
                username=self.cleaned_data['username'], 
                password=self.cleaned_data['password1']
            )
            login(self.request, auth_user)

        return user

You just need to make sure you pass in a request object when you instantiate the form. You can do that by overriding the view's get_form_kwargs method.

views.py

def get_form_kwargs(self):
    form_kwargs = super().get_form_kwargs()
    form_kwargs['request'] = self.request
    return form_kwargs

Or, make sure when you instantiate a form_class you do CustomUserCreationForm(data=request.POST, request=self.request).

Using the authenticate() and login() functions:

from django.contrib.auth import authenticate, login

def register(request):
    if request.method == 'POST':
        form = UserCreationForm(request.POST)
        if form.is_valid():
            new_user = form.save()
            messages.info(request, "Thanks for registering. You are now logged in.")
            new_user = authenticate(username=form.cleaned_data['username'],
                                    password=form.cleaned_data['password1'],
                                    )
            login(request, new_user)
            return HttpResponseRedirect("/dashboard/")