# Django 4.2.11 documentation

# Source code for django.contrib.auth

    import inspect
    import re

    from django.apps import apps as django_apps
    from django.conf import settings
    from django.core.exceptions import ImproperlyConfigured, PermissionDenied
    from django.middleware.csrf import rotate_token
    from django.utils.crypto import constant_time_compare
    from django.utils.module_loading import import_string
    from django.views.decorators.debug import sensitive_variables

    from .signals import user_logged_in, user_logged_out, user_login_failed

    SESSION_KEY = "_auth_user_id"
    BACKEND_SESSION_KEY = "_auth_user_backend"
    HASH_SESSION_KEY = "_auth_user_hash"
    REDIRECT_FIELD_NAME = "next"

    def load_backend(path):
        return import_string(path)()

    def _get_backends(return_tuples=False):
        backends = []
        for backend_path in settings.AUTHENTICATION_BACKENDS:
            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

    def get_backends():
        return _get_backends(return_tuples=False)

    @sensitive_variables("credentials")
    def _clean_credentials(credentials):
        """
        Clean a dictionary of credentials of potentially sensitive info before
        sending to less secure functions.

        Not comprehensive - intended for user_login_failed signal
        """
        SENSITIVE_CREDENTIALS = re.compile("api|token|key|secret|password|signature", re.I)
        CLEANSED_SUBSTITUTE = "********************"
        for key in credentials:
            if SENSITIVE_CREDENTIALS.search(key):
                credentials[key] = CLEANSED_SUBSTITUTE
        return credentials

    def _get_user_session_key(request):
        # This value in the session is always serialized to a string, so we need
        # to convert it back to Python whenever we access it.
        return get_user_model()._meta.pk.to_python(request.session[SESSION_KEY])

    @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 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)

    def logout(request):
        """
        Remove the authenticated user's ID from the request and flush their session
        data.
        """
        # Dispatch the signal before the user is logged out so the receivers have a
        # chance to find out *who* logged out.
        user = getattr(request, "user", None)
        if not getattr(user, "is_authenticated", True):
            user = None
        user_logged_out.send(sender=user.__class__, request=request, user=user)
        request.session.flush()
        if hasattr(request, "user"):
            from django.contrib.auth.models import AnonymousUser

            request.user = AnonymousUser()

    def get_user_model():
        """
        Return the User model that is active in this project.
        """
        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
            )

    def get_user(request):
        """
        Return the user model instance associated with the given request session.
        If no user is retrieved, return an instance of `AnonymousUser`.
        """
        from .models import AnonymousUser

        user = None
        try:
            user_id = _get_user_session_key(request)
            backend_path = request.session[BACKEND_SESSION_KEY]
        except KeyError:
            pass
        else:
            if backend_path in settings.AUTHENTICATION_BACKENDS:
                backend = load_backend(backend_path)
                user = backend.get_user(user_id)
                # Verify the session
                if hasattr(user, "get_session_auth_hash"):
                    session_hash = request.session.get(HASH_SESSION_KEY)
                    if not session_hash:
                        session_hash_verified = False
                    else:
                        session_auth_hash = user.get_session_auth_hash()
                        session_hash_verified = constant_time_compare(
                            session_hash, session_auth_hash
                        )
                    if not session_hash_verified:
                        # If the current secret does not verify the session, try
                        # with the fallback secrets and stop when a matching one is
                        # found.
                        if session_hash and any(
                            constant_time_compare(session_hash, fallback_auth_hash)
                            for fallback_auth_hash in user.get_session_auth_fallback_hash()
                        ):
                            request.session.cycle_key()
                            request.session[HASH_SESSION_KEY] = session_auth_hash
                        else:
                            request.session.flush()
                            user = None

        return user or AnonymousUser()

    def get_permission_codename(action, opts):
        """
        Return the codename of the permission for the specified action.
        """
        return "%s_%s" % (action, opts.model_name)

    def update_session_auth_hash(request, user):
        """
        Updating a user's password logs out all sessions for the user.

        Take the current request and the updated user object from which the new
        session hash will be derived and update the session hash appropriately to
        prevent a password change from logging out the session from which the
        password was changed.
        """
        request.session.cycle_key()
        if hasattr(user, "get_session_auth_hash") and request.user == user:
            request.session[HASH_SESSION_KEY] = user.get_session_auth_hash()