add handler for 403s

fixes #3104

bookwyrm/templates/403.html

@@ -0,0 +1,16 @@
+{% extends 'layout.html' %}
+{% load i18n %}
+{% load utilities %}
+
+{% block title %}{% trans "Oh no!" %}{% endblock %}
+
+{% block content %}
+<div class="block">
+    <h1 class="title">{% trans "Permission Denied" %}</h1>
+    {% blocktrans trimmed with level=request.user|get_user_permission %}
+    <p class="content">You do not have permission to view this page. Your user permission level is <code>{{ level }}</code>.</p>
+    <p class="content">If you think you should have access to this page, please speak to your BookWyrm server administrator.</p>
+    {% endblocktrans %}
+</div>
+{% endblock %}
+

bookwyrm/templatetags/utilities.py

@@ -125,3 +125,10 @@ def id_to_username(user_id):
         value = f"{name}@{domain}"
 
     return value
+
+
+@register.filter(name="get_user_permission")
+def get_user_permission(user):
+    """given a user, return their permission level"""
+
+    return user.groups.first() if user.groups.first() else "User"

bookwyrm/urls.py

@@ -792,3 +792,6 @@ urlpatterns.extend(staticfiles_urlpatterns())
 
 # pylint: disable=invalid-name
 handler500 = "bookwyrm.views.server_error"
+
+# pylint: disable=invalid-name
+handler403 = "bookwyrm.views.permission_required"

bookwyrm/views/__init__.py

@@ -167,3 +167,4 @@ from .annual_summary import (
     summary_revoke_key,
 )
 from .server_error import server_error
+from .permission_required import permission_required

bookwyrm/views/permission_required.py

@@ -0,0 +1,8 @@
+"""custom 403 handler to enable context processors"""
+from django.template.response import TemplateResponse
+
+
+def permission_required(request, exception):  # pylint: disable=unused-argument
+    """permission denied page"""
+
+    return TemplateResponse(request, "403.html")