Add setting and documentation for fixing CSRF errors (#349)

* Add documentation and setting for solving CSRF errors

* Improve proxy setup docs

* Link to reverse proxy documentation

* Fix link

bookmarks/tests/test_app_options.py

@@ -0,0 +1,29 @@
+import importlib
+import os
+from unittest import mock
+
+from django.test import TestCase
+
+
+class AppOptionsTestCase(TestCase):
+    def setUp(self) -> None:
+        self.settings_module = importlib.import_module('siteroot.settings.base')
+
+    def test_empty_csrf_trusted_origins(self):
+        module = importlib.reload(self.settings_module)
+
+        self.assertFalse(hasattr(module, 'CSRF_TRUSTED_ORIGINS'))
+
+    @mock.patch.dict(os.environ, {'LD_CSRF_TRUSTED_ORIGINS': 'https://linkding.example.com'})
+    def test_single_csrf_trusted_origin(self):
+        module = importlib.reload(self.settings_module)
+
+        self.assertTrue(hasattr(module, 'CSRF_TRUSTED_ORIGINS'))
+        self.assertCountEqual(module.CSRF_TRUSTED_ORIGINS, ['https://linkding.example.com'])
+
+    @mock.patch.dict(os.environ, {'LD_CSRF_TRUSTED_ORIGINS': 'https://linkding.example.com,http://linkding.example.com'})
+    def test_multiple_csrf_trusted_origin(self):
+        module = importlib.reload(self.settings_module)
+
+        self.assertTrue(hasattr(module, 'CSRF_TRUSTED_ORIGINS'))
+        self.assertCountEqual(module.CSRF_TRUSTED_ORIGINS, ['https://linkding.example.com', 'http://linkding.example.com'])