views: improve handling of next_url for sp initiated logout (#69740)

mellon/views.py

@@ -723,8 +723,12 @@ class LogoutView(ProfileMixin, LogMixin, View):
 
     def sp_logout_request(self, request):
         '''Launch a logout request to the identity provider'''
-        next_url = request.GET.get(REDIRECT_FIELD_NAME)
         referer = request.headers.get('Referer')
+        field_next_url = request.GET.get(REDIRECT_FIELD_NAME)
+        next_url = None
+        if field_next_url and utils.same_origin(request.build_absolute_uri(), field_next_url):
+            next_url = field_next_url
+        next_url = next_url or '/'
         if not referer or utils.same_origin(request.build_absolute_uri(), referer):
             if hasattr(request, 'user') and request.user.is_authenticated:
                 logout = None
@@ -754,7 +758,7 @@ class LogoutView(ProfileMixin, LogMixin, View):
                     self.log.info('user logged out, SLO request sent to IdP')
             else:
                 # anonymous user: if next_url is None redirect to referer
-                return HttpResponseRedirect(next_url or referer)
+                return HttpResponseRedirect(next_url)
         else:
             self.log.warning('logout refused referer %r is not of the same origin', referer)
         return HttpResponseRedirect(next_url)
@@ -774,9 +778,7 @@ class LogoutView(ProfileMixin, LogMixin, View):
             self.log.warning('partial logout')
         except lasso.Error as e:
             self.log.warning('unable to process a logout response: %s', e)
-            return HttpResponseRedirect(resolve_url(settings.LOGIN_REDIRECT_URL))
-        next_url = self.get_next_url(default=resolve_url(settings.LOGIN_REDIRECT_URL))
-        return HttpResponseRedirect(next_url)
+        return HttpResponseRedirect(self.get_next_url() or '/')
 
 
 logout = csrf_exempt(LogoutView.as_view())

tests/test_sso_slo.py

@@ -254,14 +254,16 @@ def test_sso_slo(db, app, idp, caplog, sp_settings):
 
     # again, user is already logged out
     response = app.get(reverse('mellon_logout'), extra_environ={'HTTP_REFERER': '/some/path'})
-    assert urlparse.urlparse(response['Location']).path == '/some/path'
+    assert urlparse.urlparse(response['Location']).path == '/'
 
 
 def test_sso_slo_next(db, app, idp, caplog, sp_settings):
     response = app.get(reverse('mellon_login'))
     url, body, relay_state = idp.process_authn_request_redirect(response['Location'])
     response = app.post(reverse('mellon_login'), params={'SAMLResponse': body, 'RelayState': relay_state})
-    response = app.get(reverse('mellon_logout') + '?next=/some/path/')
+    response = app.get(
+        reverse('mellon_logout') + '?next=/some/path/', extra_environ={'HTTP_REFERER': '/other/path'}
+    )
     assert urlparse.urlparse(response['Location']).path == '/singleLogout'
     url = idp.process_logout_request_redirect(response.location)
     response = app.get(url)