Authentication in Django

Django provides an authentication system, which you can combine with your own forms (UI) and different authentication backends – like username/password or OAuth.

The Django authentication model includes:

User and Group models that store user info
Views and Forms for login, logout, changing password, and more
session middleware to associate users with requests
decorators (for your view code) to require login or validate authorization
password validators for things like required minimum password length

Django Auth Docs has details with examples. The MDN Django Auth Tutorial is a great introduction.

How to Use Authentication in KU Polls

Step 1. Enable Authentication
Step 2. Add Default Redirects for KU Polls
Step 3. Create a Template for Login Page
Step 4. Add User Greeting to a Template and a link to login
Step 5. Require Login in Views a user most login to vote
Extra Material: Create a Sign-up Page for New Users, Access User Information in a View, How to Create Users, Resources

Enable Authentication

In your site’s settings.py file verify that INSTALLED_APPS includes django.contrib.auth (add it if necessary):

INSTALLED_APPS = [
    'django.contrib.admin',
    'django.contrib.auth',        <--- Authentication app
    ...
]

If you added django.contrib.auth to settings.py, you need to run makemigrations and migrate to create database tables for User and Group.

In settings.py you need two middleware components. Usually these are included by default:

MIDDLEWARE = [
    ...
    # SessionMiddleware manages sessions spanning multiple requests
    'django.contrib.sessions.middleware.SessionMiddleware',
    # AuthenticationMiddleware associates a user with session and requests
    'django.contrib.auth.middleware.AuthenticationMiddleware',
    ...
]

Enable at least one authentication backend to authenticate users.
The “ModelBackend” provides standard password-based authentication:

AUTHENTICATION_BACKENDS = [
    # username & password authentication
   'django.contrib.auth.backends.ModelBackend',  
]

In your site urls.py file, add the auth urls. By convention, accounts/ is the prefix for these URLs:

urlpatterns = [
    path('admin/', admin.site.urls),
    path('accounts/', include('django.contrib.auth.urls')),  <-- auth views
    ...,
]

django.contrib.auth.urls defines several URLs. The most important ones to get started are:

accounts/login/                  name='login'
accounts/logout/                 name='logout'

Each auth.urls has a view that provides a form named form. You need to provide a template for each view to display the form and send results back to the view.

URL                  View        Template
/accounts/login      login       templates/registration/login.html
/accounts/logout     logout      templates/registration/logged_out.html

Add Default Redirects for KU Polls

After a user “logs in”, what page should he be shown?

The default is redirect to /accounts/profile, which does not exist.

In settings.py specify defaults for login and logout. Two syntaxes:

Specify the default redirect page as a path:

LOGIN_REDIRECT_URL = '/polls/'    # after login, show list of polls
LOGOUT_REDIRECT_URL = '?'         # after logout, direct to where?

Use URL names instead of hard-coding paths. This is better:

LOGIN_REDIRECT_URL = 'polls:index'  # after login, show list of polls
LOGOUT_REDIRECT_URL = 'login' 

Note: If the login request object contains a next key, the Django login view will redirect to the URL specified by next instead of the default redirect.

Does it Work?

Rerun tests. They should still pass.
Start server and visit http://localhost:8000/accounts/asdfasdfasdfasdf/ with DEBUG=True. It should show a listing of /accounts/ URLs.
Visit the login page: http://localhost:8000/accounts/login/. What does the error message tell you?

Create directories named templates and templates/registration in your application top-level folder:

ku-polls/
    mysite/
    polls/
    templates/             <--- new directory (maybe)
        registration/      <--- new directory

In mysite/settings.py include a global templates directory:

TEMPLATES = [
    {
        # old way: 'DIRS': [os.path.join(BASE_DIR, 'templates')],
        'DIRS': [BASE_DIR / 'templates'],   # <--- global templates
        'APP_DIRS': True,
        ...
    }
]

Create a login.html template in templates/registration

ku-polls/
    templates/
        registration/
            login.html       <--- create this
            logged_out.html  <--- (do this later)

The simplest login template is:

<html>
<body>
<h2>Login</h2>
<form method="post">
  {% csrf_token %}
  {{ form.as_p }}
  <p>
  <button type="submit">Login</button>
  </p>
  <input type="hidden" name="next" value="{{next}}"/>
 </form>
 {# If you have a sign-up page, then add a link here #}
</body>
</html>

Nicer Page Template: you can render the form as an html table. You can replace form.as_p with this:

  <table>
  {{ form.as_table }}
  </table>

Test it. Start the Django server and navigate to localhost:8000/accounts/login/.
- It should show a Login form.

Create a user. Here is how to create a user with the Django interactive shell.

$ python manage.py shell

from django.contrib.auth.models import User

# username field is required, others are optional.
# Use named parameters to avoid errors.
user = User.objects.create(username='harry', 
                           email='harry@hackerone.com')
user.set_password("hackme22")
user.first_name = "Harry"
user.save()

See below for other ways to create users.

Test it: Login as this user.
Unit tests: You should write unit tests for authentication.
- Example tests: test_auth_user.py
- Copy the tests into your polls/ directory to use them.

Add User Greeting to a Template

KU Polls should show some text so a user knows that he is logged in.

In your base template or your polls index template, greet the user or ask him to login:

{% if user.is_authenticated %}
   Welcome back, {{ user.username }} 
{% else %}
   Please <a href="{% url 'login' %}?next={{request.path}}">Login</a>
{% endif %}

In the login link we added a query parameter: ?next={{request.path}}

The next=path tells Django’s login view to redirect back to this page after the user logs in. Otherwise, it will redirect him to the default LOGIN_REDIRECT_URL.
(next only works if your login.html template also passes next to the Django login view function.)

You can require a user to login to access some views. In KU Polls, we require a user to login in order to vote.

Before your vote view add the @login_required annotation:

from django.contrib.auth.decorators import login_required

@login_required
def vote(request, question_id):
    """Vote for a choice on a question (poll)."""

Test it. If you are not logged in, when you try to submit a vote you should be directed to the login page.

Two Other Ways to require login in views:

For a class-based view use the LoginRequired Mixin.

from django.contrib.auth.mixins import LoginRequiredMixin

class DetailView(LoginRequiredMixin, generic.DetailView):
    """Class based view for viewing a poll."""
    model = Question
    template_name = 'polls/detail.html'

Use Python Code. The request parameter always contains a user attribute, even if no one is logged in.

def vote(request, question_id):
    """Vote for a choice on a question (poll)."""
    user = request.user
    if not user.is_authenticated:
       return redirect('login')

Extra Material

These steps describe how to enable visitors to create their own local account. In most apps it is better to use OAuth so that visitors can login using their Google, Github, Facebook, etc., account.
Enabling OAuth is suprisingly easy to do in Django.

To enable visitors to create a local account:

define a url for a “Sign up” page
create a view to handle this page
create a page template for the sign-up page

In your project urls.py file add a “signup/” url:

urlpatterns = [
   ...
   path('accounts/', include('django.contrib.auth.urls')), 
   path('signup/', views.signup, name='signup')
]

Create a view to handle the signup URL. Put this views.py in the same directory as urls.py (e.g. mysite). Add this function in views.py.

from django.shortcuts import render, redirect
from django.contrib.auth import login, authenticate
from django.contrib.auth.forms import UserCreationForm
   
def signup(request):
    """Register a new user."""
    if request.method == 'POST':
        form = UserCreationForm(request.POST)
        if form.is_valid():
            form.save()
            # get named fields from the form data
            username = form.cleaned_data.get('username')
            # password input field is named 'password1'
            raw_passwd = form.cleaned_data.get('password1')
            user = authenticate(username=username,password=raw_passwd)
            login(request, user)
           return redirect('polls:index')
        # what if form is not valid?
        # we should display a message in signup.html
    else:
        # create a user form and display it the signup page
        form = UserCreationForm()
    return render(request, 'registration/signup.html', {'form': form})

The important thing here is that the view uses Django’s UserCreationForm, and passes this form to the template for rendering. UserCreationForm provides code to validate and clean input data.

Create a signup.html template containing a sign up form. The signup view (above) renders this template when the user visits /signup, and re-renders the page if a POST request finds any problems in the form data.
In templates/registration/signup.html write:

<h2>Register</h2>
<form method="POST">
    {% csrf_token %}
    <table style="padding: 2ex;">
    {{ form.as_table }}     {# this line shows the sign-up form #}
    <tr>
    <td colspan="2">
    <button type="submit">Register</button>
    </td>
    </tr>
    </table>
</form>

The important parts of this template are

render the form: form.as_table
POST submits the form back to the same URL that the request came from (since there is no action=... parameter)

Access User Information in a View

The logged in user is saved as part of the session and included in the request object (HttpRequest), which is passed to every view.

def vote(request, question_id):
    """Vote for one of the answers to a question."""
    user = request.user
    print("current user is", user.id, "login", user.username)
    print("Real name:", user.first_name, user.last_name)

Access User Information in a Template

Show the username in your templates. If a visitor is not logged in, then show a link to Login.

If you have a global base template, add this to the base template.

Inside page templates access user information, such as:

{{ user }}                     - reference to user object, never null
{% if user.is_authenticated %} - true if user is logged in
{{ user.username }}            - the user login name or empty string
{{ user.first_name }}          - may be an empty string 

How to Create Users

You can use these methods in a Python function or the Django shell.

User.objects.create_user convenience method:

from django.contrib.auth.models import User

# Use named parameters to avoid errors.
# username and email fields are required, others are optional.
user = User.objects.create_user( 'username', 
          email='email@some.domain', 
          password='password')

# set optional attributes
user.first_name = "Harry"
user.last_name = "Hacker"
user.save()

User.objects.create method:

user = User.objects.create(username='username', 
                           email='email@some.domain') 
user.set_password("secret")
user.first_name = "Harry"
user.save()

Other ways to create users are:

add a registration or “sign-up” page to your app
the admin interface
use a data fixture and manage.py loaddata to read user data from a file

URLs in Django’s `auth` Application

Django’s auth app provides views for each of these URLs:

accounts/login/                  [name='login']
accounts/logout/                 [name='logout']
accounts/password_change/        [name='password_change']
accounts/password_change/done/   [name='password_change_done']
accounts/password_reset/         [name='password_reset']
accounts/password_reset/done/    [name='password_reset_done']
accounts/reset/<uidb64>/<token>/ [name='password_reset_confirm']
accounts/reset/done/             [name='password_reset_complete']

to use these views you must create a template for the view you want in a folder named templates/registration.
The templates should have the same name as the view name: the login view expects a template named login.html. The login view encapsulates its data in a Form named form, so in your login.html template do something like this:

<form method="POST">
  {% csrf_token %}
  <table style="padding: 2ex;">
  {{ form.as_table }}
  </table>
  <button type="submit">Login</button>
  <!-- if your app redirects user to login before accessing some pages, then next contains return url -->
  <input type="hidden" name="next" value="{{next}}" />
</form>

Django’s Password Validators

Django provides a collection of validators for authentication data.
They are defined in settings.py, usually:

# settings.py
AUTH_PASSWORD_VALIDATORS = [
    {
        'NAME': 'django.contrib.auth.password_validation.UserAttributeSimilarityValidator',
    },
    {
        'NAME': 'django.contrib.auth.password_validation.MinimumLengthValidator',
    },
    {
        'NAME': 'django.contrib.auth.password_validation.CommonPasswordValidator',
    },
    {
        'NAME': 'django.contrib.auth.password_validation.NumericPasswordValidator',
    },
]

These password requirements are good but sometimes annoying. You can customize them.

Look at the constructors for the password validator classes in the file django/contribe/auth/password_validation.py. Each constructor has some named parameters. You can specify parameter values to customize the validators.

Validator	Constructor Parameters
MinimumLengthValidator	`min_length=0`
UserAttributeSimilarityValidator	`user_attributes=[...],max_similarity=0.7`
CommonPasswordValidator	`password_list_path=path-to-file`
NumericPasswordValidator	none

NumericPasswordValidator checks if a password is purely alphanumeric (disallowed). If you want to allow alphanumeric passwords, comment out the validator.

Resources

Django User Authentication System https://docs.djangoproject.com/en/2.2/topics/auth/default/.

User Authentication and Permissions in the MDN Django Tutorial, Part 8. This tutorial is very good, with more explanation than the Django official tutorial.

William Vincent Django Sign Up Tutorial shows another way of implementing a “Sign Up” view as a separate app. He uses a class-based view for sign-up which is very simple.

William Vincent Login/Logout Tutorial has same info as this doc but also uses a base.html to structure page templates.