Fixed #31790 -- Fixed setting SameSite and Secure cookies flags in HttpResponse.delete_cookie().

Cookies with the "SameSite" flag set to None and without the "secure"
flag will be soon rejected by latest browser versions.

This affects sessions and messages cookies.

django/contrib/messages/storage/cookie.py

@@ -92,7 +92,11 @@ class CookieStorage(BaseStorage):
                 samesite=settings.SESSION_COOKIE_SAMESITE,
             )
         else:
-            response.delete_cookie(self.cookie_name, domain=settings.SESSION_COOKIE_DOMAIN)
+            response.delete_cookie(
+                self.cookie_name,
+                domain=settings.SESSION_COOKIE_DOMAIN,
+                samesite=settings.SESSION_COOKIE_SAMESITE,
+            )
 
     def _store(self, messages, response, remove_oldest=True, *args, **kwargs):
         """

django/contrib/sessions/middleware.py

@@ -42,6 +42,7 @@ class SessionMiddleware(MiddlewareMixin):
                 settings.SESSION_COOKIE_NAME,
                 path=settings.SESSION_COOKIE_PATH,
                 domain=settings.SESSION_COOKIE_DOMAIN,
+                samesite=settings.SESSION_COOKIE_SAMESITE,
             )
             patch_vary_headers(response, ('Cookie',))
         else:

django/http/response.py

@@ -210,13 +210,18 @@ class HttpResponseBase:
         value = signing.get_cookie_signer(salt=key + salt).sign(value)
         return self.set_cookie(key, value, **kwargs)
 
-    def delete_cookie(self, key, path='/', domain=None):
-        # Most browsers ignore the Set-Cookie header if the cookie name starts
-        # with __Host- or __Secure- and the cookie doesn't use the secure flag.
-        secure = key.startswith(('__Secure-', '__Host-'))
+    def delete_cookie(self, key, path='/', domain=None, samesite=None):
+        # Browsers can ignore the Set-Cookie header if the cookie doesn't use
+        # the secure flag and:
+        # - the cookie name starts with "__Host-" or "__Secure-", or
+        # - the samesite is "none".
+        secure = (
+            key.startswith(('__Secure-', '__Host-')) or
+            (samesite and samesite.lower() == 'none')
+        )
         self.set_cookie(
             key, max_age=0, path=path, domain=domain, secure=secure,
-            expires='Thu, 01 Jan 1970 00:00:00 GMT',
+            expires='Thu, 01 Jan 1970 00:00:00 GMT', samesite=samesite,
         )
 
     # Common methods used by subclasses

docs/ref/request-response.txt

@@ -890,7 +890,7 @@ Methods
 
         Using ``samesite='None'`` (string) was allowed.
 
-.. method:: HttpResponse.delete_cookie(key, path='/', domain=None)
+.. method:: HttpResponse.delete_cookie(key, path='/', domain=None, samesite=None)
 
     Deletes the cookie with the given key. Fails silently if the key doesn't
     exist.
@@ -899,6 +899,10 @@ Methods
     values you used in ``set_cookie()`` -- otherwise the cookie may not be
     deleted.
 
+    .. versionchanged:: 2.2.15
+
+        The ``samesite`` argument was added.
+
 .. method:: HttpResponse.close()
 
     This method is called at the end of the request directly by the WSGI

docs/releases/2.2.15.txt

@@ -0,0 +1,17 @@
+===========================
+Django 2.2.15 release notes
+===========================
+
+*Expected August 3, 2020*
+
+Django 2.2.15 fixes a bug in 2.2.14.
+
+Bugfixes
+========
+
+* Allowed setting the ``SameSite`` cookie flag in
+  :meth:`.HttpResponse.delete_cookie` (:ticket:`31790`).
+
+* Fixed setting the ``Secure`` cookie flag in
+  :meth:`.HttpResponse.delete_cookie` for cookies that use ``samesite='none'``
+  (:ticket:`31790`).

docs/releases/3.0.9.txt

@@ -9,4 +9,9 @@ Django 3.0.9 fixes several bugs in 3.0.8.
 Bugfixes
 ========
 
-* ...
+* Allowed setting the ``SameSite`` cookie flag in
+  :meth:`.HttpResponse.delete_cookie` (:ticket:`31790`).
+
+* Fixed setting the ``Secure`` cookie flag in
+  :meth:`.HttpResponse.delete_cookie` for cookies that use ``samesite='none'``
+  (:ticket:`31790`).

docs/releases/index.txt

@@ -55,6 +55,7 @@ versions of the documentation contain the release notes for any later releases.
 .. toctree::
    :maxdepth: 1
 
+   2.2.15
    2.2.14
    2.2.13
    2.2.12

tests/messages_tests/test_cookie.py

@@ -1,5 +1,6 @@
 import json
 
+from django.conf import settings
 from django.contrib.messages import constants
 from django.contrib.messages.storage.base import Message
 from django.contrib.messages.storage.cookie import (
@@ -85,6 +86,10 @@ class CookieTests(BaseTests, SimpleTestCase):
         self.assertEqual(response.cookies['messages'].value, '')
         self.assertEqual(response.cookies['messages']['domain'], '.example.com')
         self.assertEqual(response.cookies['messages']['expires'], 'Thu, 01 Jan 1970 00:00:00 GMT')
+        self.assertEqual(
+            response.cookies['messages']['samesite'],
+            settings.SESSION_COOKIE_SAMESITE,
+        )
 
     def test_get_bad_cookie(self):
         request = self.get_request()

tests/responses/test_cookie.py

@@ -105,6 +105,7 @@ class DeleteCookieTests(SimpleTestCase):
         self.assertEqual(cookie['path'], '/')
         self.assertEqual(cookie['secure'], '')
         self.assertEqual(cookie['domain'], '')
+        self.assertEqual(cookie['samesite'], '')
 
     def test_delete_cookie_secure_prefix(self):
         """
@@ -118,3 +119,14 @@ class DeleteCookieTests(SimpleTestCase):
                 cookie_name = '__%s-c' % prefix
                 response.delete_cookie(cookie_name)
                 self.assertIs(response.cookies[cookie_name]['secure'], True)
+
+    def test_delete_cookie_secure_samesite_none(self):
+        # delete_cookie() sets the secure flag if samesite='none'.
+        response = HttpResponse()
+        response.delete_cookie('c', samesite='none')
+        self.assertIs(response.cookies['c']['secure'], True)
+
+    def test_delete_cookie_samesite(self):
+        response = HttpResponse()
+        response.delete_cookie('c', samesite='lax')
+        self.assertEqual(response.cookies['c']['samesite'], 'lax')

tests/sessions_tests/tests.py

@@ -758,8 +758,9 @@ class SessionMiddlewareTests(TestCase):
         #  Set-Cookie: sessionid=; expires=Thu, 01 Jan 1970 00:00:00 GMT; Max-Age=0; Path=/
         self.assertEqual(
             'Set-Cookie: {}=""; expires=Thu, 01 Jan 1970 00:00:00 GMT; '
-            'Max-Age=0; Path=/'.format(
+            'Max-Age=0; Path=/; SameSite={}'.format(
                 settings.SESSION_COOKIE_NAME,
+                settings.SESSION_COOKIE_SAMESITE,
             ),
             str(response.cookies[settings.SESSION_COOKIE_NAME])
         )
@@ -789,8 +790,9 @@ class SessionMiddlewareTests(TestCase):
         #              Path=/example/
         self.assertEqual(
             'Set-Cookie: {}=""; Domain=.example.local; expires=Thu, '
-            '01 Jan 1970 00:00:00 GMT; Max-Age=0; Path=/example/'.format(
+            '01 Jan 1970 00:00:00 GMT; Max-Age=0; Path=/example/; SameSite={}'.format(
                 settings.SESSION_COOKIE_NAME,
+                settings.SESSION_COOKIE_SAMESITE,
             ),
             str(response.cookies[settings.SESSION_COOKIE_NAME])
         )