✨(backend) support Agent Connect Logout flow

The default Logout view provided by Mozilla Django OIDC is not suitable
for the Agent Connect Logout flow.

Previously, when a user was logging-out, only its Django session was ended.
However, its session in the OIDC provider was still active.

Agent Connect implements a 'session/end' endpoint, that allows services to
end user session when they logout.

Agent Connect logout triggers cannot work with the default views implemented
by the dependency Mozilla Django OIDC. In their implementation, they decided
to end Django Session before redirecting to the OIDC provider.

The Django session needs to be retained during the logout process.

An OIDC state is saved to the request session, pass to Agent Connect Logout
endpoint, and verified when the backend receives the Logout callback from Agent
Connect. It seems to follow OIDC specifications.

If for any reason, the Logout flow cannot be initiated with Agent Connect,
(missing ID token in cache, unauthenticated user, etc), the user is redirected
to the final URL, without interacting with Agent Connect.

src/backend/core/tests/authentication/test_urls.py

@@ -0,0 +1,10 @@
+"""Unit tests for the Authentication URLs."""
+
+from core.authentication.urls import urlpatterns
+
+
+def test_urls_override_default_mozilla_django_oidc():
+    """Custom URL patterns should override default ones from Mozilla Django OIDC."""
+
+    url_names = [u.name for u in urlpatterns]
+    assert url_names.index("oidc_logout_custom") < url_names.index("oidc_logout")

src/backend/core/tests/authentication/test_views.py

@@ -0,0 +1,231 @@
+"""Unit tests for the Authentication Views."""
+
+from unittest import mock
+from urllib.parse import parse_qs, urlparse
+
+from django.contrib.auth.models import AnonymousUser
+from django.contrib.sessions.middleware import SessionMiddleware
+from django.core.exceptions import SuspiciousOperation
+from django.test import RequestFactory
+from django.test.utils import override_settings
+from django.urls import reverse
+from django.utils import crypto
+
+import pytest
+from rest_framework.test import APIClient
+
+from core import factories
+from core.authentication.views import OIDCLogoutCallbackView, OIDCLogoutView
+
+pytestmark = pytest.mark.django_db
+
+
+@override_settings(LOGOUT_REDIRECT_URL="/example-logout")
+def test_view_logout_anonymous():
+    """Anonymous users calling the logout url,
+    should be redirected to the specified LOGOUT_REDIRECT_URL."""
+
+    url = reverse("oidc_logout_custom")
+    response = APIClient().get(url)
+
+    assert response.status_code == 302
+    assert response.url == "/example-logout"
+
+
+@mock.patch.object(
+    OIDCLogoutView, "construct_oidc_logout_url", return_value="/example-logout"
+)
+def test_view_logout(mocked_oidc_logout_url):
+    """Authenticated users should be redirected to OIDC provider for logout."""
+
+    user = factories.UserFactory()
+
+    client = APIClient()
+    client.force_login(user)
+
+    url = reverse("oidc_logout_custom")
+    response = client.get(url)
+
+    mocked_oidc_logout_url.assert_called_once()
+
+    assert response.status_code == 302
+    assert response.url == "/example-logout"
+
+
+@override_settings(LOGOUT_REDIRECT_URL="/default-redirect-logout")
+@mock.patch.object(
+    OIDCLogoutView, "construct_oidc_logout_url", return_value="/default-redirect-logout"
+)
+def test_view_logout_no_oidc_provider(mocked_oidc_logout_url):
+    """Authenticated users should be logged out when no OIDC provider is available."""
+
+    user = factories.UserFactory()
+
+    client = APIClient()
+    client.force_login(user)
+
+    url = reverse("oidc_logout_custom")
+
+    with mock.patch("mozilla_django_oidc.views.auth.logout") as mock_logout:
+        response = client.get(url)
+        mocked_oidc_logout_url.assert_called_once()
+        mock_logout.assert_called_once()
+
+    assert response.status_code == 302
+    assert response.url == "/default-redirect-logout"
+
+
+@override_settings(LOGOUT_REDIRECT_URL="/example-logout")
+def test_view_logout_callback_anonymous():
+    """Anonymous users calling the logout callback url,
+    should be redirected to the specified LOGOUT_REDIRECT_URL."""
+
+    url = reverse("oidc_logout_callback")
+    response = APIClient().get(url)
+
+    assert response.status_code == 302
+    assert response.url == "/example-logout"
+
+
+@pytest.mark.parametrize(
+    "initial_oidc_states",
+    [{}, {"other_state": "foo"}],
+)
+def test_view_logout_persist_state(initial_oidc_states):
+    """State value should be persisted in session's data."""
+
+    user = factories.UserFactory()
+
+    request = RequestFactory().request()
+    request.user = user
+
+    middleware = SessionMiddleware(get_response=lambda x: x)
+    middleware.process_request(request)
+
+    if initial_oidc_states:
+        request.session["oidc_states"] = initial_oidc_states
+        request.session.save()
+
+    mocked_state = "mock_state"
+
+    OIDCLogoutView().persist_state(request, mocked_state)
+
+    assert "oidc_states" in request.session
+    assert request.session["oidc_states"] == {
+        "mock_state": {},
+        **initial_oidc_states,
+    }
+
+
+@override_settings(OIDC_OP_LOGOUT_ENDPOINT="/example-logout")
+@mock.patch.object(OIDCLogoutView, "persist_state")
+@mock.patch.object(crypto, "get_random_string", return_value="mocked_state")
+def test_view_logout_construct_oidc_logout_url(
+    mocked_get_random_string, mocked_persist_state
+):
+    """Should construct the logout URL to initiate the logout flow with the OIDC provider."""
+
+    user = factories.UserFactory()
+
+    request = RequestFactory().request()
+    request.user = user
+
+    middleware = SessionMiddleware(get_response=lambda x: x)
+    middleware.process_request(request)
+
+    request.session["oidc_id_token"] = "mocked_oidc_id_token"
+    request.session.save()
+
+    redirect_url = OIDCLogoutView().construct_oidc_logout_url(request)
+
+    mocked_persist_state.assert_called_once()
+    mocked_get_random_string.assert_called_once()
+
+    params = parse_qs(urlparse(redirect_url).query)
+
+    assert params["id_token_hint"][0] == "mocked_oidc_id_token"
+    assert params["state"][0] == "mocked_state"
+
+    url = reverse("oidc_logout_callback")
+    assert url in params["post_logout_redirect_uri"][0]
+
+
+@override_settings(LOGOUT_REDIRECT_URL="/")
+def test_view_logout_construct_oidc_logout_url_none_id_token():
+    """If no ID token is available in the session,
+    the user should be redirected to the final URL."""
+
+    user = factories.UserFactory()
+
+    request = RequestFactory().request()
+    request.user = user
+
+    middleware = SessionMiddleware(get_response=lambda x: x)
+    middleware.process_request(request)
+
+    redirect_url = OIDCLogoutView().construct_oidc_logout_url(request)
+
+    assert redirect_url == "/"
+
+
+@pytest.mark.parametrize(
+    "initial_state",
+    [None, {"other_state": "foo"}],
+)
+def test_view_logout_callback_wrong_state(initial_state):
+    """Should raise an error if OIDC state doesn't match session data."""
+
+    user = factories.UserFactory()
+
+    request = RequestFactory().request()
+    request.user = user
+
+    middleware = SessionMiddleware(get_response=lambda x: x)
+    middleware.process_request(request)
+
+    if initial_state:
+        request.session["oidc_states"] = initial_state
+        request.session.save()
+
+    callback_view = OIDCLogoutCallbackView.as_view()
+
+    with pytest.raises(SuspiciousOperation) as excinfo:
+        callback_view(request)
+
+    assert (
+        str(excinfo.value) == "OIDC callback state not found in session `oidc_states`!"
+    )
+
+
+@override_settings(LOGOUT_REDIRECT_URL="/example-logout")
+def test_view_logout_callback():
+    """If state matches, callback should clear OIDC state and redirects."""
+
+    user = factories.UserFactory()
+
+    request = RequestFactory().get("/logout-callback/", data={"state": "mocked_state"})
+    request.user = user
+
+    middleware = SessionMiddleware(get_response=lambda x: x)
+    middleware.process_request(request)
+
+    mocked_state = "mocked_state"
+
+    request.session["oidc_states"] = {mocked_state: {}}
+    request.session.save()
+
+    callback_view = OIDCLogoutCallbackView.as_view()
+
+    with mock.patch("mozilla_django_oidc.views.auth.logout") as mock_logout:
+
+        def clear_user(request):
+            # Assert state is cleared prior to logout
+            assert request.session["oidc_states"] == {}
+            request.user = AnonymousUser()
+
+        mock_logout.side_effect = clear_user
+        response = callback_view(request)
+        mock_logout.assert_called_once()
+
+    assert response.status_code == 302
+    assert response.url == "/example-logout"