I had a similar requirement where either username/email should work for the username field.In case someone is looking for the authentication backend way of doing this,check out the following working code.You can change the queryset if you desire only the email.

from django.contrib.auth import get_user_model  # gets the user_model django  default or your own custom
from django.contrib.auth.backends import ModelBackend
from django.db.models import Q


# Class to permit the athentication using email or username
class CustomBackend(ModelBackend):  # requires to define two functions authenticate and get_user

    def authenticate(self, username=None, password=None, **kwargs):
        UserModel = get_user_model()

        try:
            # below line gives query set,you can change the queryset as per your requirement
            user = UserModel.objects.filter(
                Q(username__iexact=username) |
                Q(email__iexact=username)
            ).distinct()

        except UserModel.DoesNotExist:
            return None

        if user.exists():
            ''' get the user object from the underlying query set,
            there will only be one object since username and email
            should be unique fields in your models.'''
            user_obj = user.first()
            if user_obj.check_password(password):
                return user_obj
            return None
        else:
            return None

    def get_user(self, user_id):
        UserModel = get_user_model()
        try:
            return UserModel.objects.get(pk=user_id)
        except UserModel.DoesNotExist:
            return None

Also add AUTHENTICATION_BACKENDS = ( ‘path.to.CustomBackend’, ) in settings.py

You should customize ModelBackend class.
My simple code:

from django.contrib.auth.backends import ModelBackend
from django.contrib.auth import get_user_model

class YourBackend(ModelBackend):

  def authenticate(self, username=None, password=None, **kwargs):
    UserModel = get_user_model()
    if username is None:
        username = kwargs.get(UserModel.USERNAME_FIELD)
    try:
        if '@' in username:
            UserModel.USERNAME_FIELD = 'email'
        else:
            UserModel.USERNAME_FIELD = 'username'

        user = UserModel._default_manager.get_by_natural_key(username)
    except UserModel.DoesNotExist:
        UserModel().set_password(password)
    else:
        if user.check_password(password) and self.user_can_authenticate(user):
            return user

And in settings.py file, add:

AUTHENTICATION_BACKENDS = ['path.to.class.YourBackend']

If you’re starting a new project, django highly recommended you to set up a custom user model. (see https://docs.djangoproject.com/en/dev/topics/auth/customizing/#using-a-custom-user-model-when-starting-a-project)

and if you did it, add three lines to your user model:

class MyUser(AbstractUser):
    USERNAME_FIELD = 'email'
    email = models.EmailField(_('email address'), unique=True) # changes email to unique and blank to false
    REQUIRED_FIELDS = [] # removes email from REQUIRED_FIELDS

Then authenticate(email=email, password=password) works, while authenticate(username=username, password=password) stops working.

from django.contrib.auth.models import User

from django.db import Q

class EmailAuthenticate(object):

    def authenticate(self, username=None, password=None, **kwargs):
        try:
            user = User.objects.get(Q(email=username) | Q(username=username))
        except User.DoesNotExist:
            return None
        except MultipleObjectsReturned:
            return User.objects.filter(email=username).order_by('id').first()

        if user.check_password(password):
            return user
        return None

    def get_user(self,user_id):
        try:
            return User.objects.get(pk=user_id)
        except User.DoesNotExist:
            return None

And then in settings.py:

AUTHENTICATION_BACKENDS = (
  'articles.backends.EmailAuthenticate',
)

where articles is my django-app, backends.py is the python file inside my app and EmailAuthenticate is the authentication backend class inside my backends.py file

For Django 2

username = get_object_or_404(User, email=data["email"]).username
        user = authenticate(
            request, 
            username = username, 
            password = data["password"]
        )
        login(request, user)

Django 4.0

There are two main ways you can implement email authentication, taking note of the following:

• emails should not be unique on a user model to mitigate misspellings and malicious use.
• emails should only be used for authentication if they are verified (as in we have sent a verification email and they have clicked the verify link).
• We should only send emails to verified email addresses.

Custom User Model

A custom user model is recommended when starting a new project as changing mid project can be tricky.

We will add an email_verified field to restrict email authentication to users with a verified email address.

# app.models.py
from django.db import models
from django.contrib.auth.models import AbstractUser


class User(AbstractUser):
    email_verified = models.BooleanField(default=False)

We will then create a custom authentication backend that will substitute a given email address for a username.

This backend will work with authentication forms that explicitly set an email field as well as those setting a username field.

# app.backends.py
from django.contrib.auth import get_user_model
from django.contrib.auth.backends import ModelBackend
from django.db.models import Q

UserModel = get_user_model()


class CustomUserModelBackend(ModelBackend):
    def authenticate(self, request, username=None, password=None, **kwargs):
        if username is None:
            username = kwargs.get(UserModel.USERNAME_FIELD, kwargs.get(UserModel.EMAIL_FIELD))
        if username is None or password is None:
            return
        try:
            user = UserModel._default_manager.get(
                Q(username__exact=username) | (Q(email__iexact=username) & Q(email_verified=True))
            )
        except UserModel.DoesNotExist:
            # Run the default password hasher once to reduce the timing
            # difference between an existing and a nonexistent user (#20760).
            UserModel().set_password(password)
        else:
            if user.check_password(password) and self.user_can_authenticate(user):
                return user

We then modify our projects settings.py to use our custom user model and authentication backend.

# project.settings.py

AUTH_USER_MODEL = "app.User"
AUTHENTICATION_BACKENDS = ["app.backends.CustomUserModelBackend"]

Be sure that you run manage.py makemigrations before you migrate and that the first migration contains these settings.

Extended User Model

While less performant than a custom User model (requires a secondary query), it may be better to extend the existing User model in an existing project and may be preferred depending on login flow and verification process.

We create a one-to-one relation from EmailVerification to whichever User model our project is using through the AUTH_USER_MODEL setting.

# app.models.py
from django.conf import settings
from django.db import models


class EmailVerification(models.Model):
    user = models.OneToOneField(
        settings.AUTH_USER_MODEL,
        on_delete=models.CASCADE,
        related_query_name="verification"
    )
    verified = models.BooleanField(default=False)

We can also create a custom admin that includes our extension inline.

# app.admin.py
from django.contrib import admin
from django.contrib.auth import get_user_model
from django.contrib.auth.admin import UserAdmin as BaseUserAdmin

from .models import EmailVerification

UserModel = get_user_model()


class VerificationInline(admin.StackedInline):
    model = EmailVerification
    can_delete = False
    verbose_name_plural = 'verification'


class UserAdmin(BaseUserAdmin):
    inlines = (VerificationInline,)


admin.site.unregister(UserModel)
admin.site.register(UserModel, UserAdmin)

We then create a backend similar to the one above that simply checks the related models verified field.

# app.backends.py
from django.contrib.auth import get_user_model
from django.contrib.auth.backends import ModelBackend
from django.db.models import Q

UserModel = get_user_model()


class ExtendedUserModelBackend(ModelBackend):
    def authenticate(self, request, username=None, password=None, **kwargs):
        if username is None:
            username = kwargs.get(UserModel.USERNAME_FIELD, kwargs.get(UserModel.EMAIL_FIELD))
        if username is None or password is None:
            return
        try:
            user = UserModel._default_manager.get(
                Q(username__exact=username) | (Q(email__iexact=username) & Q(verification__verified=True))
            )
        except UserModel.DoesNotExist:
            # Run the default password hasher once to reduce the timing
            # difference between an existing and a nonexistent user (#20760).
            UserModel().set_password(password)
        else:
            if user.check_password(password) and self.user_can_authenticate(user):
                return user

We then modify our projects settings.py to use our authentication backend.

# project.settings.py

AUTHENTICATION_BACKENDS = ["app.backends.ExtendedUserModelBackend"]

You can then makemigrations and migrate to add functionality to an existing project.

Notes

• if usernames are case insensitive change Q(username__exact=username) to Q(username__iexact=username).
• In production prevent a new user registering with an existing verified email address.

Email and Username Authentication for Django 2.X

Having in mind that this is a common question, here’s a custom implementation mimicking the Django source code but that authenticates the user with either username or email, case-insensitively, keeping the timing attack protection and not authenticating inactive users.

from django.contrib.auth.backends import ModelBackend, UserModel
from django.db.models import Q

class CustomBackend(ModelBackend):
    def authenticate(self, request, username=None, password=None, **kwargs):
        try:
            user = UserModel.objects.get(Q(username__iexact=username) | Q(email__iexact=username))
        except UserModel.DoesNotExist:
            UserModel().set_password(password)
        else:
            if user.check_password(password) and self.user_can_authenticate(user):
                return user

    def get_user(self, user_id):
        try:
            user = UserModel.objects.get(pk=user_id)
        except UserModel.DoesNotExist:
            return None

        return user if self.user_can_authenticate(user) else None

Always remember to add it your settings.py the correct Authentication Backend.

Authentication with Email and Username For Django 2.x

from django.contrib.auth import get_user_model
from django.contrib.auth.backends import ModelBackend
from django.db.models import Q

class EmailorUsernameModelBackend(ModelBackend):
    def authenticate(self, request, username=None, password=None, **kwargs):
        UserModel = get_user_model()
        try:
            user = UserModel.objects.get(Q(username__iexact=username) | Q(email__iexact=username))
        except UserModel.DoesNotExist:
            return None
        else:
            if user.check_password(password):
                return user
        return None

In settings.py, add following line,

AUTHENTICATION_BACKENDS = ['appname.filename.EmailorUsernameModelBackend']

Authentication with Email For Django 2.x

def admin_login(request):
if request.method == "POST":
    email = request.POST.get('email', None)
    password = request.POST.get('password', None)
    try:
        get_user_name = CustomUser.objects.get(email=email)
        user_logged_in =authenticate(username=get_user_name,password=password)
        if user_logged_in is not None:
            login(request, user_logged_in)
            messages.success(request, f"WelcomeBack{user_logged_in.username}")
            return HttpResponseRedirect(reverse('backend'))
        else:
            messages.error(request, 'Invalid Credentials')
            return HttpResponseRedirect(reverse('admin_login'))
    except:
        messages.warning(request, 'Wrong Email')
        return HttpResponseRedirect(reverse('admin_login'))

else:
    if request.user.is_authenticated:
        return HttpResponseRedirect(reverse('backend'))
    return render(request, 'login_panel/login.html')

Email authentication for Django 3.x

For using email/username and password for authentication instead of the default username and password authentication, we need to override two methods of ModelBackend class: authenticate() and get_user():

The get_user method takes a user_id – which could be a username, database ID or whatever, but has to be unique to your user object – and returns a user object or None. If you have not kept email as a unique key, you will have to take care of multiple result returned for the query_set. In the below code, this has been taken care of by returning the first user from the returned list.

from django.contrib.auth.backends import ModelBackend, UserModel
from django.db.models import Q

class EmailBackend(ModelBackend):
    def authenticate(self, request, username=None, password=None, **kwargs):
        try: #to allow authentication through phone number or any other field, modify the below statement
            user = UserModel.objects.get(Q(username__iexact=username) | Q(email__iexact=username))
        except UserModel.DoesNotExist:
            UserModel().set_password(password)
        except MultipleObjectsReturned:
            return User.objects.filter(email=username).order_by('id').first()
        else:
            if user.check_password(password) and self.user_can_authenticate(user):
                return user

    def get_user(self, user_id):
        try:
            user = UserModel.objects.get(pk=user_id)
        except UserModel.DoesNotExist:
            return None

        return user if self.user_can_authenticate(user) else None

By default, AUTHENTICATION_BACKENDS is set to:

['django.contrib.auth.backends.ModelBackend']

In settings.py file, add following at the bottom to override the default:

AUTHENTICATION_BACKENDS = ('appname.filename.EmailBackend',)

If You created Custom database, from there if you want to validate your email id and password.

1. Fetch the Email id and Password with models.objects.value_list('db_columnname').filter(db_emailname=textbox email)

2.assign in list fetched object_query_list

3.Convert List to String

Ex :

1. Take the Html Email_id and Password Values in Views.py

   u_email = request.POST.get('uemail')

   u_pass = request.POST.get('upass')

2. Fetch the Email id and password from the database

   Email = B_Reg.objects.values_list('B_Email',flat=True).filter(B_Email=u_email)

   Password = B_Reg.objects.values_list('Password',flat=True).filter(B_Email=u_email)

3. Take the Email id and password values in the list from the Query value set

   Email_Value = Email[0]

   Password_Value=Password[0]

4. Convert list to String

   string_email = ''.join(map(str, Email_Value))

   string_password = ''.join(map(str, Password_Value))

Finally your Login Condition

if (string_email==u_email and string_password ==u_pass)

I have created a helper for that: function authenticate_user(email, password).

from django.contrib.auth.models import User


def authenticate_user(email, password):
    try:
        user = User.objects.get(email=email)
    except User.DoesNotExist:
        return None
    else:
        if user.check_password(password):
            return user

    return None

class LoginView(View):
    template_name = 'myapp/login.html'

    def get(self, request):
        return render(request, self.template_name)

    def post(self, request):
        email = request.POST['email']
        password = request.POST['password']
        user = authenticate_user(email, password)
        context = {}

        if user is not None:
            if user.is_active:
                login(request, user)

                return redirect(self.request.GET.get('next', '/'))
            else:
                context['error_message'] = "user is not active"
        else:
            context['error_message'] = "email or password not correct"

        return render(request, self.template_name, context)

Pretty simple. There is no need for any additional classes.

When you create and update a user with an email, just set the username field with the email.

That way when you authenticate the username field will be the same value of the email.

The code:

# Create
User.objects.create_user(username=post_data['email'] etc...)

# Update
user.username = post_data['email']
user.save()

# When you authenticate
user = authenticate(username=post_data['email'], password=password)

It seems that the method of doing this has been updated with Django 3.0.

A working method for me has been:

authentication.py # <– I placed this in an app (did not work in the project folder alongside settings.py

from django.contrib.auth import get_user_model
from django.contrib.auth.backends import BaseBackend
from django.contrib.auth.hashers import check_password
from django.contrib.auth.models import User

class EmailBackend(BaseBackend):
    def authenticate(self, request, username=None, password=None, **kwargs):
        UserModel = get_user_model()
        try:
            user = UserModel.objects.get(email=username)
        except UserModel.DoesNotExist:
            return None
        else:
            if user.check_password(password):
                return user
        return None

    def get_user(self, user_id):
        UserModel = get_user_model()
        try:
            return UserModel.objects.get(pk=user_id)
        except UserModel.DoesNotExist:
            return None

Then added this to the settings.py file

AUTHENTICATION_BACKENDS = (
    'appname.authentication.EmailBackend',
)

The default user model inherits/ Extends an Abstract class. The framework should be lenient to a certain amount of changes or alterations.

A simpler hack is to do the following:
This is in a virtual environment

1. Go to your django installation location and find the Lib folder
2. navigate to django/contrib/auth/
3. find and open the models.py file. Find the AbstractUser class line 315

LINE 336 on the email attribute add unique and set it to true

email = models.EmailField(_('email address'), blank=True,unique=True)

USERNAME_FIELD = 'email'
REQUIRED_FIELDS = ['username']

5. Done, makemigrations & migrate

Do this at you own risk,

May, 2022 Update:

This instruction shows how to set up authentication with "email" and "password" instead of "username" and "password" and in this instruction, "username" is removed and I tried not to change the default Django settings as much as possible.

First, run the command below to create "account" application:

python manage.py startapp account

Then, set "account" application to "INSTALLED_APPS" and set AUTH_USER_MODEL = ‘account.CustomUser’ in "settings.py" as shown below:

# "settings.py"

INSTALLED_APPS = [
    # ...
    "account", # Here
]

AUTH_USER_MODEL = 'account.CustomUser' # Here

Then, create "managers.py" just under "account" folder and create "CustomUserManager" class extending "UserManager" class in "managers.py" as shown below. *Just copy & paste the code below to "managers.py" and "managers.py" is necessary to make the command "python manage.py createsuperuser" work properly without any error:

# "account/managers.py"

from django.contrib.auth.models import UserManager
from django.contrib.auth.hashers import make_password

class CustomUserManager(UserManager): # Here
   
    def _create_user(self, email, password, **extra_fields):
        
        if not email:
            raise ValueError("The given email must be set")
        email = self.normalize_email(email)
        user = self.model(email=email, **extra_fields)
        user.password = make_password(password)
        user.save(using=self._db)
        return user

    def create_user(self, email=None, password=None, **extra_fields):
        extra_fields.setdefault("is_staff", False)
        extra_fields.setdefault("is_superuser", False)
        return self._create_user(email, password, **extra_fields)

    def create_superuser(self, email=None, password=None, **extra_fields):
        extra_fields.setdefault("is_staff", True)
        extra_fields.setdefault("is_superuser", True)

        if extra_fields.get("is_staff") is not True:
            raise ValueError("Superuser must have is_staff=True.")
        if extra_fields.get("is_superuser") is not True:
            raise ValueError("Superuser must have is_superuser=True.")

        return self._create_user(email, password, **extra_fields)

Then, create "CustomUser" class extending "AbstractUser" class and remove "username" by setting it "None" and set "email" with "unique=True" and set "email" to "USERNAME_FIELD" and set "CustomUserManager" class to "objects" in "account/models.py" as shown below. *Just copy & paste the code below to "account/models.py":

# "account/models.py"

from django.db import models
from django.contrib.auth.models import AbstractUser
from .managers import CustomUserManager

class CustomUser(AbstractUser):
    username = None # Here
    email = models.EmailField('email address', unique=True) # Here
    
    USERNAME_FIELD = 'email' # Here
    REQUIRED_FIELDS = []

    objects = CustomUserManager() # Here

    class Meta:
        verbose_name = "custom user"
        verbose_name_plural = "custom users"

Or, you can also create "CustomUser" class extending "AbstractBaseUser" and "PermissionsMixin" classes as shown below. *This code below with "AbstractBaseUser" and "PermissionsMixin" classes is equivalent to the code above with "AbstractUser" class and as you can see, the code above with "AbstractUser" class is much less code:

from django.db import models
from django.contrib.auth.models import AbstractBaseUser, PermissionsMixin
from django.utils import timezone
from .managers import CustomUserManager

class CustomUser(AbstractBaseUser, PermissionsMixin):
    first_name = models.CharField("first name", max_length=150, blank=True)
    last_name = models.CharField("last name", max_length=150, blank=True)
    email = models.EmailField('email address', unique=True)
    is_staff = models.BooleanField(
        "staff status",
        default=False,
        help_text="Designates whether the user can log into this admin site.",
    )
    is_active = models.BooleanField(
        "active",
        default=True,
        help_text=
            "Designates whether this user should be treated as active. "
            "Unselect this instead of deleting accounts."
        ,
    )
    date_joined = models.DateTimeField("date joined", default=timezone.now)

    USERNAME_FIELD = 'email'

    objects = CustomUserManager() # Here

Then, create "forms.py" just under "account" folder and create "CustomUserCreationForm" class extending "UserCreationForm" class and "CustomUserChangeForm" class extending "UserChangeForm" class and set "CustomUser" class to "model" in "Meta" inner class in "CustomUserCreationForm" and "CustomUserChangeForm" classes in "account/forms.py" as shown below. *Just copy & paste the code below to "forms.py":

# "account/forms.py"

from django.contrib.auth.forms import UserCreationForm, UserChangeForm
from .models import CustomUser

class CustomUserCreationForm(UserCreationForm):

    class Meta:
        model = CustomUser
        fields = ('email',)

class CustomUserChangeForm(UserChangeForm):

    class Meta:
        model = CustomUser
        fields = ('email',)

Then, create "CustomUserAdmin" class extending "UserAdmin" class and set "CustomUserCreationForm" and "CustomUserChangeForm" classes to "add_form" and "form" respectively and set "AdminPasswordChangeForm" class to "change_password_form" then set "CustomUser" and "CustomUserAdmin" classes to "admin.site.register()" in "account/admin.py" as shown below. *Just copy & paste the code below to "account/admin.py":

from django.contrib import admin
from .forms import CustomUserCreationForm, CustomUserChangeForm
from django.contrib.auth.forms import AdminPasswordChangeForm
from django.contrib.auth.admin import UserAdmin
from .models import CustomUser

class CustomUserAdmin(UserAdmin):
    fieldsets = (
        (None, {"fields": ("password",)}),
        ("Personal info", {"fields": ("first_name", "last_name", "email")}),
        (
            "Permissions",
            {
                "fields": (
                    "is_active",
                    "is_staff",
                    "is_superuser",
                    "groups",
                    "user_permissions",
                ),
            },
        ),
        ("Important dates", {"fields": ("last_login", "date_joined")}),
    )
    add_fieldsets = (
        (
            None,
            {
                "classes": ("wide",),
                "fields": ("email", "password1", "password2"),
            },
        ),
    )
    add_form = CustomUserCreationForm # Here
    form = CustomUserChangeForm # Here
    change_password_form = AdminPasswordChangeForm # Here
    list_display = ("email", "first_name", "last_name", "is_staff")
    list_filter = ("is_staff", "is_superuser", "is_active", "groups")
    search_fields = ("first_name", "last_name", "email")
    ordering = ("email",)
    filter_horizontal = (
        "groups",
        "user_permissions",
    )

admin.site.register(CustomUser, CustomUserAdmin) # Here

Then, run the command below to make migrations and migrate:

python manage.py makemigrations && python manage.py migrate

Then, run the command below to create a superuser:

python manage.py createsuperuser

Then, run the command below to run a server:

python manage.py runserver 0.0.0.0:8000

Then, open the url below:

http://localhost:8000/admin/login/

Finally, you can log in with "email" and "password" as shown below:

And this is "Add custom user" page as shown below:

All of these are horrendously complicated for what should be a simple problem.

Check that a user exists with that email, then get that user’s username for the argument in Django’s authenticate() method.

try:
    user = User.objects.get(email = request_dict['email'])
    user = authenticate(username = user.username, password = request_dict['password'])
except:
    return HttpResponse('User not found.', status = 400)