Django Auth应用实现用户身份认证

def authenticate(request=None, **credentials):
    #__get_backends获取当前系统中定义的认证后端，并依次迭代
    for backend, backend_path in _get_backends(return_tuples=True):
        try:
            inspect.getcallargs(backend.authenticate, request, **credentials)
        except TypeError:
            #此后端不接受这些凭据作为参数。返回继续执行循环
            continue
        try:
             #通过当前的认证后端尝试获取 User，若获取不到就会抛出异常！
            user = backend.authenticate(request, **credentials)
        except PermissionDenied:
            #抛出异常Permission
            break
         #如果没有返回，继续执行下一个认证
        if user is None:
            continue
        #添加一个属性标志，代表后端认证成功
        user.backend = backend_path
        return user
    # 所提供的凭据对所有后端、触发信号无效
    user_login_failed.send(sender=__name__, credentials=_clean_credentials(credentials), request=request)

def _get_backends(return_tuples=False):
    backends = []
    #AUTHENTICATION_BACKENDS 定义了当前系统可以用的身份认证列表
    for backend_path in settings.AUTHENTICATION_BACKENDS:
        #加载后端
        backend = load_backend(backend_path)
        backends.append((backend, backend_path) if return_tuples else backend)
    #如果未定义后端列表抛出异常
    if not backends:
        raise ImproperlyConfigured(
            'No authentication backends have been defined. Does '
            'AUTHENTICATION_BACKENDS contain anything?'
        )
    return backends

AUTHENTICATION_BACKENDS=['django.contib.auth.backends.ModelBackend']  #当前系统默认认证后端ModelBackend

def get_user_model():
    """
    返回一个处于激活状态的 User
    """
    try:
        return django_apps.get_model(settings.AUTH_USER_MODEL, require_ready=False)
    except ValueError:
        raise ImproperlyConfigured("AUTH_USER_MODEL must be of the form 'app_label.model_name'")
    except LookupError:
        raise ImproperlyConfigured(
            "AUTH_USER_MODEL refers to model '%s' that has not been installed" % settings.AUTH_USER_MODEL
        )

# 使用默认User model时
>>> from django.contrib.auth import get_user_model
>>> get_user_model()
<class 'django.contrib.auth.models.User'>
# 使用自定义User model时
>>> from django.contrib.auth import get_user_model
>>> get_user_model()
<class 'xxx.models.NewUser'>
# get_user_model()实际获取的是settings.AUTH_USER_MODEL指定的User model

#格式： "<django_app名>.<model名>"
AUTH_USER_MODEL = "appname.NewUser" 
#在models.py编写示例
from django.conf import settings
from django.db import models
class Article(models.Model):
    author = models.ForeignKey(settings.AUTH_USER_MODEL)
    title = models.CharField(max_length=100)