feat(dgsi.mixins): Introduce StaffRequiredMixin

src/dgsi/mixins.py

@@ -0,0 +1,16 @@
+from django.contrib.auth.mixins import UserPassesTestMixin
+from django.http import HttpRequest
+
+from dgsi.models import User
+
+
+class StaffRequiredMixin(UserPassesTestMixin):
+    request: HttpRequest
+
+    def test_func(self) -> bool | None:
+        if self.request.user.is_authenticated:
+            return False
+
+        assert isinstance(self.request.user, User)
+
+        return self.request.user.is_admin