Added the unauthorized method to the UserUtilityInterface interface, so that when the user has not logged in, the permission decorator can ask the user to log in instead of failing with HTTP 403 Forbidden.

src/accounting/utils/permission.py

@@ -21,7 +21,7 @@ This module should not import any other module from the application.
 """
 import typing as t
 
-from flask import abort, Blueprint
+from flask import abort, Blueprint, Response
 
 from accounting.utils.user import get_current_user, UserUtilityInterface
 
@@ -49,6 +49,10 @@ def has_permission(rule: t.Callable[[], bool]) -> t.Callable:
             :raise Forbidden: When the user is denied.
             """
             if not rule():
+                if get_current_user() is None:
+                    response: Response | None = _unauthorized_func()
+                    if response is not None:
+                        return response
                 abort(403)
             return view(*args, **kwargs)
 
@@ -66,6 +70,9 @@ data."""
 __can_admin_func: t.Callable[[], bool] = lambda: True
 """The callback that returns whether the current user can administrate the
 accounting settings."""
+_unauthorized_func: t.Callable[[], Response | None] \
+    = lambda: Response(status=403)
+"""The callback that returns the response to require the user to log in."""
 
 
 def can_view() -> bool:
@@ -111,10 +118,12 @@ def init_app(bp: Blueprint, user_utils: UserUtilityInterface) -> None:
     :param user_utils: The user utilities.
     :return: None.
     """
-    global __can_view_func, __can_edit_func, __can_admin_func
+    global __can_view_func, __can_edit_func, __can_admin_func, \
+        _unauthorized_func
     __can_view_func = user_utils.can_view
     __can_edit_func = user_utils.can_edit
     __can_admin_func = user_utils.can_admin
+    _unauthorized_func = user_utils.unauthorized
     bp.add_app_template_global(user_utils.can_view, "accounting_can_view")
     bp.add_app_template_global(user_utils.can_edit, "accounting_can_edit")
     bp.add_app_template_global(user_utils.can_admin, "accounting_can_admin")

src/accounting/utils/user.py

@@ -23,7 +23,7 @@ import typing as t
 from abc import ABC, abstractmethod
 
 import sqlalchemy as sa
-from flask import g
+from flask import g, Response
 from flask_sqlalchemy.model import Model
 
 T = t.TypeVar("T", bound=Model)
@@ -59,6 +59,17 @@ class UserUtilityInterface(t.Generic[T], ABC):
             accounting settings, or False otherwise.
         """
 
+    @abstractmethod
+    def unauthorized(self) -> Response | None:
+        """Returns the response to require the user to log in.
+
+        This may be a redirection to the login page, or an HTTP 401
+        Unauthorized response for HTTP Authentication.  If this returns None,
+        an HTTP 403 Forbidden response is return to the user.
+
+        :return: The response to require the user to log in.
+        """
+
     @property
     @abstractmethod
     def cls(self) -> t.Type[T]: