自定义后端，您需要指定 get_user 函数。请参阅文档。 get_user 实现可以简单地使用现有的User表，就像您这样：

  def get_user（self，user_id）：
尝试：
返回User.objects.get（pk = user_id）
除了User.DoesNotExist：
返回None 
 

之所以需要这样做，是因为在某些情况下，您需要通过用户主键从其他来源获取用户

I would like to create an authentication backend that allows users to log_in only using their email (no username, no password).

Here is what I tried.

backends.py:

from django.conf import settings
from django.contrib.auth.models import User

class EmailAuthBackend(object):    
    def authenticate(self, username=None, password=None):
        try:
            user = User.objects.get(email=username)
            if user:
                return user
        except User.DoesNotExist:
            return None 

settings.py:

  AUTHENTICATION_BACKENDS = (
       'path_to.backends.EmailAuthBackend',
       'django.contrib.auth.backends.ModelBackend',
      )

html:

   <form  method="post" action="{% url myproject.views.test %}">
    {% csrf_token %}

        <input type="text" name="email" value=""/>

    <button type="submit">Valider</button>

    </form>

view:

 def test(request):
    email = ''
    if 'email' in request.POST:
        email = request.POST.get('email')
        if not User.objects.filter(email=email):
            User.objects.create(email=email)
        user = authenticate(username=email)
        if user is not None:
            if user.is_active:
                auth_login(request, user)
    return HttpResponseRedirect(reverse('home'))

It doesn't work, the user is not authenticated. And I also have this error when I go to the /admin:

    AttributeError at /admin/logout/
    'EmailAuthBackend' object has no attribute 'get_user'

For each custom backend in Django, you need to specify the get_user function. See the documentation. The get_user implementation can simply use the existing User table, like you are:

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

The reason this is required is for situations where you'd need to fetch the User via its primary key from a different source.