🐛 — Allow to use SHA1-signed anonymous edit URL

The default django.core.signing Signer uses SHA256 algorithm since Django 3.
Umap used Django 2 in the paste, so people had SHA1 signed anonymous edit URLs,
which became unusable when umap switch to Django 3.
This commit makes them usable again (the new SHA256-signed anonymous edit URLs
still works, obviously).

umap/tests/test_map_views.py

@@ -4,6 +4,7 @@ import pytest
 from django.contrib.auth import get_user_model
 from django.urls import reverse
 
+from django.core.signing import Signer
 from umap.models import DataLayer, Map
 
 from .base import login_required
@@ -401,6 +402,20 @@ def test_anonymous_edit_url(cookieclient, anonymap):
     assert key in cookieclient.cookies
 
 
+@pytest.mark.usefixtures('allow_anonymous')
+def test_sha1_anonymous_edit_url(cookieclient, anonymap):
+    signer = Signer(algorithm='sha1')
+    signature = signer.sign(anonymap.pk)
+    url = reverse('map_anonymous_edit_url', kwargs={'signature': signature})
+    canonical = reverse('map', kwargs={'pk': anonymap.pk,
+                                       'slug': anonymap.slug})
+    response = cookieclient.get(url)
+    assert response.status_code == 302
+    assert response['Location'] == canonical
+    key, value = anonymap.signed_cookie_elements
+    assert key in cookieclient.cookies
+
+
 @pytest.mark.usefixtures('allow_anonymous')
 def test_bad_anonymous_edit_url_should_return_403(cookieclient, anonymap):
     url = anonymap.get_anonymous_edit_url()

umap/views.py

@@ -654,11 +654,15 @@ class MapAnonymousEditUrl(RedirectView):
 
     def get(self, request, *args, **kwargs):
         signer = Signer()
+        try:
+            pk = signer.unsign(self.kwargs["signature"])
+        except BadSignature:
+            signer = Signer(algorithm='sha1')
             try:
                 pk = signer.unsign(self.kwargs["signature"])
             except BadSignature:
                 return HttpResponseForbidden()
-        else:
+
         map_inst = get_object_or_404(Map, pk=pk)
         url = map_inst.get_absolute_url()
         response = HttpResponseRedirect(url)