Django自定义认证系统原理及源码分析解读

疑问

Django在如何自定义用户登录认证系统的时候大家都会里面立马说 自定义一个 或者多个backend比如通过账号+密码、邮箱+密码邮箱+验证码、手机号+短信验证码等等。 然后设置 在settings中配置一个 AUTHENTICATION_BACKENDS就行。

但是为什么要这么做呢？ 原理是什么呢？

今天就带大家分析一波Django的认证相关的源码逻辑告诉你为什么要这么做。

关于认证登录

结论预告 >>>>

Django 默认的认证保持功能主要是通过 用户名+密码 发送给后端之后会先去通过 authenticate 函数验证 用户名和密码是否正确； 如果正确则进行 login 登录login字后会把对应的用户 user 存入到session中。并且request.user 为当前 user（而不是默认的 AnonymousUser

所以Django的认证核心是两步

# 验证用户
user = auth.authenticate(username=username, password=password)
# 然后登录
auth.login(request, user)

源码解读

对于Django自带的管理后台的登录首先要明确几个点

1、自定义的应用都是通过 admin.site.register() 注册到 Admin后台去的

2、对于Django自带的 admin 应用它也是把自己注册到 AdminSite 中去的 （源码位置： django/contrib/admin.sites.py 中 AdminSite类的 __init__() 方法中

Django新增项目之后在项目目录下的urls.py 文件配置的所有项目的路由地址入口后续新增的应用的也都是通过这里进行include配置。

# proj/urls.py
urlpatterns = [
    path('admin/', admin.site.urls),
]

Django自带后台的登录地址 http://127.0.0.1:8000/admin/login 所以登录逻辑入口就是 admin.site.urls

定位登录入口

从源码 django/contrib/admin.sites.py 中

class AdminSite:
    ... ...
    def get_urls(self):
        ... ...
        # Admin-site-wide views.
        urlpatterns = [
            path('', wrap(self.index), name='index'),
            path('login/', self.login, name='login'),
            ... ...
        ]
            
    @property
    def urls(self):
        return self.get_urls(), 'admin', self.name
    
    ... ...
    @never_cache
    def login(self, request, extra_context=None):
        ... ...
        from django.contrib.admin.forms import AdminAuthenticationForm
        from django.contrib.auth.views import LoginView
        ... ...
        defaults = {
            'extra_context': context,
            # 这里 self.login_form为空 所以 authentication_form是 AdminAuthenticationForm
            'authentication_form': self.login_form or AdminAuthenticationForm,
            'template_name': self.login_template or 'admin/login.html',
        }
        request.current_app = self.name
        return LoginView.as_view(**defaults)(request)

admin.site.urls 最终调用 get_urls() 方法 在该方法中定义了 login 路由对应的视图函数是self.login。

然后查阅login函数发现它返回的是 LoginView 类视图 来源于 django.contrib.auth.views

另外这里也需要注意下 django.contrib.admin.forms.AdminAuthenticationForm 因为最后实际登录的时候用到的Form表单就是这个

重点看LoginView视图

# django/contrib/auth/views.py
class LoginView(SuccessURLAllowedHostsMixin, FormView):
    """
    Display the login form and handle the login action.
    """
    form_class = AuthenticationForm
    authentication_form = None
    redirect_field_name = REDIRECT_FIELD_NAME
    template_name = 'registration/login.html'
    redirect_authenticated_user = False
    extra_context = None

    @method_decorator(sensitive_post_parameters())
    @method_decorator(csrf_protect)
    @method_decorator(never_cache)
    def dispatch(self, request, *args, **kwargs):
        if self.redirect_authenticated_user and self.request.user.is_authenticated:
            redirect_to = self.get_success_url()
            if redirect_to == self.request.path:
                raise ValueError(
                    "Redirection loop for authenticated user detected. Check that "
                    "your LOGIN_REDIRECT_URL doesn't point to a login page."
                )
            return HttpResponseRedirect(redirect_to)
        return super().dispatch(request, *args, **kwargs)

    def get_success_url(self):
        url = self.get_redirect_url()
        return url or resolve_url(settings.LOGIN_REDIRECT_URL)

    def get_redirect_url(self):
        """Return the user-originating redirect URL if it's safe."""
        redirect_to = self.request.POST.get(
            self.redirect_field_name,
            self.request.GET.get(self.redirect_field_name, '')
        )
        url_is_safe = url_has_allowed_host_and_scheme(
            url=redirect_to,
            allowed_hosts=self.get_success_url_allowed_hosts(),
            require_https=self.request.is_secure(),
        )
        return redirect_to if url_is_safe else ''

    def get_form_class(self):
        return self.authentication_form or self.form_class

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

    def form_valid(self, form):
        """Security check complete. Log the user in."""
        auth_login(self.request, form.get_user())
        return HttpResponseRedirect(self.get_success_url())

这里 SuccessURLAllowedHostsMixin 可以先忽略（它是判断允许那些主机来访问URL

LoginView继承自 FormView FormView 继承自 TemplateResponseMixin 和 BaseFormView而BaseFormView又继承自FormMixin 和 ProcessFormView

# django/views/generic/edit.py
class ProcessFormView(View):
    """Render a form on GET and processes it on POST."""
    def get(self, request, *args, **kwargs):
        """Handle GET requests: instantiate a blank version of the form."""
        return self.render_to_response(self.get_context_data())

    def post(self, request, *args, **kwargs):
        """
        Handle POST requests: instantiate a form instance with the passed
        POST variables and then check if it's valid.
        """
        form = self.get_form()
        if form.is_valid():
            return self.form_valid(form)
        else:
            return self.form_invalid(form)



class BaseFormView(FormMixin, ProcessFormView):
    """A base view for displaying a form."""


class FormView(TemplateResponseMixin, BaseFormView):
    """A view for displaying a form and rendering a template response."""

同样的TemplateResponseMixin是定义返回结果格式的一个Mixin可以先忽略。

定位Post

我们知道 login 最终发送的是一个 post 请求。

对于Django 类视图的请求解析路径大概流程是：

1 通过XxxxView.as_view() 最终到 View 类（位于 django/views/generic/base.py中 请求 as_view 方法

2as_view方法中调用 setup() 方法 setup() 方法初始化 request/args/kwargs 参数 这里划个**重点**

3然后在as_view方法中继续调用 dispatch() 方法该方法获取handler这个handler就是最终调用方法

http_method_names = ['get', 'post', 'put', 'patch', 'delete', 'head', 'options', 'trace']

所以通过继承关系知道最终 post 调用的是 ProcessFormView类中的方法

这里先 获取 form 然后判断 form的有效性通过之后执行form_valid(form)

表单详解

然后我们拆开来分析上面的简单的三个步骤

获取form表单

通过上面的源码知道了 BaseFormView 继承 FormMixin 和 ProcessFormView 两个类 在 ProcessFormView 中的post中使用了 self.get_form() 方法 该方法其实位于 FormMixin类

# django/views/generic/edit.py
class FormMixin(ContextMixin):
    """Provide a way to show and handle a form in a request."""
    initial = {}
    form_class = None
    success_url = None
    prefix = None
	... ...

    def get_form_class(self):
        """Return the form class to use."""
        return self.form_class

    def get_form(self, form_class=None):
        """Return an instance of the form to be used in this view."""
        if form_class is None:
            form_class = self.get_form_class()
        return form_class(**self.get_form_kwargs())

特别注意📢

1ProcessFormView 中的Post 方法中 form = self.get_form() 是没有参数的所以在 FormMixin 中的 get_form() 中获取 form_class的时候 是通过

form_class = self.get_form_class()

2但是在 LoginView中 该方法被覆盖了

def get_form_class(self):
        return self.authentication_form or self.form_class

3另外讲到在 基类 View中 setup 方法会设置 kwargs 等参数

4回忆在最开始的LoginView 中

LoginView.as_view(**defaults)(request)

这里的 **defautls 中有个 authentication_form 的值是 AdminAuthenticationForm

所以虽然 LoginView类的最开始定义了 form_class 是 AuthenticationForm

class LoginView:
    form_class = AuthenticationForm
    authentication_form = None

但是 authentication_form 通过 setup() 方法被赋值了然后 LoginView中的 get_form_class是先判断获取 authentication_form的。

所以最终 Django Admin后台登录的时候 form_class 是 AdminAuthenticationForm

但其实阅读源码不难发现AdminAuthenticationForm 是继承自 AuthenticationForm的

# django/contrib/admin/forms.py
class AdminAuthenticationForm(AuthenticationForm):
    """
    A custom authentication form used in the admin app.
	... ... 

而 AdminAuthenticationForm 类中只定义了 confirm_login_allowed 方法其他方法使用的还是父类的方法比如 clean() 方法这里也划**重点**哦

判断form有效性

对于 form对象的 is_valid() 方法该方法一般都是对于 Form基类中很少被重写

从上面知道目前的 form 对象对AdminAuthenticationForm类的对象而 AdminAuthenticationForm 继承 AuthenticationForm AuthenticationForm 也没有重写 is_valid 方法所以得知 is_valid() 方法存在于基类BaseForm 中 （AuthenticationForm(forms.Form) 而 Form基础自BaseForm

# django/forms/forms.py
class Form(BaseForm, metaclass=DeclarativeFieldsMetaclass):
    "A collection of Fields, plus their associated data."

    
class BaseForm:
	... ...
    @property
    def errors(self):
        """Return an ErrorDict for the data provided for the form."""
        if self._errors is None:
            self.full_clean()
        return self._errors

    def is_valid(self):
        """Return True if the form has no errors, or False otherwise."""
        print("lcDebug-> here is_valid?")
        return self.is_bound and not self.errors

    def full_clean(self):
        """
        Clean all of self.data and populate self._errors and self.cleaned_data.
        """
        self._errors = ErrorDict()
        if not self.is_bound:  # Stop further processing.
            return
        self.cleaned_data = {}
        # If the form is permitted to be empty, and none of the form data has
        # changed from the initial data, short circuit any validation.
        if self.empty_permitted and not self.has_changed():
            return

        self._clean_fields()
        self._clean_form()
        self._post_clean()

    def _clean_form(self):
        try:
            cleaned_data = self.clean()
        except ValidationError as e:
            self.add_error(None, e)
        else:
            if cleaned_data is not None:
                self.cleaned_data = cleaned_data
    ... ...

1从上述源码看到 is_valid() 方法检查 self.is_bound 和 self.errors

2errors() 这里是个方法如果表单没有问题的时候执行 self.full_clean()方法

3full_clean 方法中重点关注 self._clean_form() 方法

4_clean_form() 方法中 cleaned_data = self.clean()

还记得在获取表单那个小章节划的重点么？ form类的clean() 方法这个方法是在 AuthenticationForm 类中被重写的

from django.contrib.auth import (
    authenticate, get_user_model, password_validation,
)

class AuthenticationForm(forms.Form):
    """
    Base class for authenticating users. Extend this to get a form that accepts
    username/password logins.
    """
    username = UsernameField(widget=forms.TextInput(attrs={'autofocus': True}))
    password = forms.CharField(
        label=_("Password"),
        strip=False,
        widget=forms.PasswordInput(attrs={'autocomplete': 'current-password'}),
    )

    error_messages = {
        'invalid_login': _(
            "Please enter a correct %(username)s and password. Note that both "
            "fields may be case-sensitive."
        ),
        'inactive': _("This account is inactive."),
    }

    def __init__(self, request=None, *args, **kwargs):
        ... ...

    def clean(self):
        username = self.cleaned_data.get('username')
        password = self.cleaned_data.get('password')

        if username is not None and password:
            self.user_cache = authenticate(self.request, username=username, password=password)
            if self.user_cache is None:
                raise self.get_invalid_login_error()
            else:
                self.confirm_login_allowed(self.user_cache)

        return self.cleaned_data

查阅 clean() 方法源码看到在通过 self.cleaned_data （self.cleaned_data 的赋值是在 BaseForm的 self._clean_fields 方法中完成的获取用户名和密码之后如果不为空就进行**认证authenticate**

而这里的 authenticate方法 来自于 django/crontrib/auth/__init__.py

# django/contrib/auth/__init__.py

@sensitive_variables('credentials')
def authenticate(request=None, **credentials):
    """
    If the given credentials are valid, return a User object.
    """
    for backend, backend_path in _get_backends(return_tuples=True):
        backend_signature = inspect.signature(backend.authenticate)
        try:
            backend_signature.bind(request, **credentials)
        except TypeError:
            # This backend doesn't accept these credentials as arguments. Try the next one.
            continue
        try:
            user = backend.authenticate(request, **credentials)
        except PermissionDenied:
            # This backend says to stop in our tracks - this user should not be allowed in at all.
            break
        if user is None:
            continue
        # Annotate the user object with the path of the backend.
        user.backend = backend_path
        return user

    # The credentials supplied are invalid to all backends, fire signal
    user_login_failed.send(sender=__name__, credentials=_clean_credentials(credentials), request=request)
    
def _get_backends(return_tuples=False):
    backends = []
    for backend_path in settings.AUTHENTICATION_BACKENDS:
        # print("backend: ", backend_path)
        backend = load_backend(backend_path)
        backends.append((backend, backend_path) if return_tuples else backend)
    if not backends:
        raise ImproperlyConfigured(
            'No authentication backends have been defined. Does '
            'AUTHENTICATION_BACKENDS contain anything?'
        )
    return backends

核心源码

user = backend.authenticate(request, **credentials)

会获取 所有的 backends 进行遍历利用对应的backend中的 authenticate 方法进行认证

通过 _get_backends 方法知道默认获取的是 settings.AUTHENTICATION_BACKENDS

# django/conf/global_settings.py
AUTHENTICATION_BACKENDS = ['django.contrib.auth.backends.ModelBackend']

ModelBackend 类源码

# django/contrib/auth/backends.py
class ModelBackend(BaseBackend):
    """
    Authenticates against settings.AUTH_USER_MODEL.
    """

    def authenticate(self, request, username=None, password=None, **kwargs):
        if username is None:
            username = kwargs.get(UserModel.USERNAME_FIELD)
        if username is None or password is None:
            return
        try:
            user = UserModel._default_manager.get_by_natural_key(username)
        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

看到最终是通过默认的 ModelBackend类的 authenticate 认证对应的用户名和密码然后 返回对应的 user 对象

简单来讲就是

form.is_valid() 方法调用了 form.clean() 方法在 form.clean() 方法中调用了 对应的 authenticate() 方法该方法查找可能得backends利用对应的backend的authenticate() 方法返回user对象

form_valid 表单

验证完毕 form表单有效性并且完成了 authenticate认证得到了 user对象。

然后调用 form_valid(form) 方法通过源码知道该方法是在LoginView中被重写

# django/contrib/auth/views.py

from django.contrib.auth import  login as auth_login
class LoginView:
    ... ...
        def form_valid(self, form):
        """Security check complete. Log the user in."""
        auth_login(self.request, form.get_user())
        return HttpResponseRedirect(self.get_success_url())

看到这里实际是调用了 auth_login 进行了用户登录登录成功进行跳转

# django/contrib/auth/__init__.py
def login(request, user, backend=None):
    """
    Persist a user id and a backend in the request. This way a user doesn't
    have to reauthenticate on every request. Note that data set during
    the anonymous session is retained when the user logs in.
    """
    session_auth_hash = ''
    if user is None:
        user = request.user
    if hasattr(user, 'get_session_auth_hash'):
        session_auth_hash = user.get_session_auth_hash()

    if SESSION_KEY in request.session:
        if _get_user_session_key(request) != user.pk or (
                session_auth_hash and
                not constant_time_compare(request.session.get(HASH_SESSION_KEY, ''), session_auth_hash)):
            # To avoid reusing another user's session, create a new, empty
            # session if the existing session corresponds to a different
            # authenticated user.
            request.session.flush()
    else:
        request.session.cycle_key()

    try:
        backend = backend or user.backend
    except AttributeError:
        backends = _get_backends(return_tuples=True)
        if len(backends) == 1:
            _, backend = backends[0]
        else:
            raise ValueError(
                'You have multiple authentication backends configured and '
                'therefore must provide the `backend` argument or set the '
                '`backend` attribute on the user.'
            )
    else:
        if not isinstance(backend, str):
            raise TypeError('backend must be a dotted import path string (got %r).' % backend)

    request.session[SESSION_KEY] = user._meta.pk.value_to_string(user)
    request.session[BACKEND_SESSION_KEY] = backend
    request.session[HASH_SESSION_KEY] = session_auth_hash
    if hasattr(request, 'user'):
        request.user = user
    rotate_token(request)
    user_logged_in.send(sender=user.__class__, request=request, user=user)

这里login函数的核心是 通过 authenticate 的到的 user 对象然后

1 设置相关的session值用于后续的判断处理

2通过 user_logged_in 信号去更新 用户的 last_login 字段（如果有的话

---

截止当前通过源码解读大家应该能回答最开始的问题了哈。

也希望带着大家进行源码解读让大家更好的理解Django的原理。

同时作为优秀的框架源码分析学习也是有助于我们学习如何高效开发、组织代码提高自己的开发质量。