[3.0.x] Fixed #31790 -- Fixed setting SameSite cookies flag 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.

Backport of 240cbb63bf9965c63d7a3cc9032f91410f414d46 from master.

10 files changed, 44 insertions, 7 deletions

diff --git a/django/contrib/messages/storage/cookie.py b/django/contrib/messages/storage/cookie.py
index 9e0c93e436..057d573d3f 100644
--- a/django/contrib/messages/storage/cookie.py
+++ b/django/contrib/messages/storage/cookie.py
@@ -89,7 +89,11 @@ 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):
         """
diff --git a/django/contrib/sessions/middleware.py b/django/contrib/sessions/middleware.py
index d36be4eca8..7a0f9e030b 100644
--- a/django/contrib/sessions/middleware.py
+++ b/django/contrib/sessions/middleware.py
@@ -38,6 +38,7 @@ 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:
diff --git a/django/http/response.py b/django/http/response.py
index c33feb97c4..d98c040d91 100644
--- a/django/http/response.py
+++ b/django/http/response.py
@@ -209,13 +209,13 @@ 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):
+    def delete_cookie(self, key, path='/', domain=None, samesite=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-'))
         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
diff --git a/docs/ref/request-response.txt b/docs/ref/request-response.txt
index 619ade110d..8eb578d505 100644
--- a/docs/ref/request-response.txt
+++ b/docs/ref/request-response.txt
@@ -858,7 +858,7 @@ Methods
     you will need to remember to pass it to the corresponding
     :meth:`HttpRequest.get_signed_cookie` call.
 
-.. 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.
@@ -867,6 +867,10 @@ 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
diff --git a/docs/releases/2.2.15.txt b/docs/releases/2.2.15.txt
new file mode 100644
index 0000000000..df26962029
--- /dev/null
+++ b/docs/releases/2.2.15.txt
@@ -0,0 +1,13 @@
+===========================
+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`).
diff --git a/docs/releases/3.0.9.txt b/docs/releases/3.0.9.txt
index adc0f30b10..36bcf4546f 100644
--- a/docs/releases/3.0.9.txt
+++ b/docs/releases/3.0.9.txt
@@ -9,4 +9,5 @@ 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`).
diff --git a/docs/releases/index.txt b/docs/releases/index.txt
index 434789de1f..6b9674005f 100644
--- a/docs/releases/index.txt
+++ b/docs/releases/index.txt
@@ -41,6 +41,7 @@ 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
diff --git a/tests/messages_tests/test_cookie.py b/tests/messages_tests/test_cookie.py
index 211d33f04c..7456e03a70 100644
--- a/tests/messages_tests/test_cookie.py
+++ b/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()
diff --git a/tests/responses/test_cookie.py b/tests/responses/test_cookie.py
index a46d910f34..3470e9bf28 100644
--- a/tests/responses/test_cookie.py
+++ b/tests/responses/test_cookie.py
@@ -102,6 +102,7 @@ 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):
         """
@@ -115,3 +116,8 @@ class DeleteCookieTests(SimpleTestCase):
                 cookie_name = '__%s-c' % prefix
                 response.delete_cookie(cookie_name)
                 self.assertEqual(response.cookies[cookie_name]['secure'], True)
+
+    def test_delete_cookie_samesite(self):
+        response = HttpResponse()
+        response.delete_cookie('c', samesite='lax')
+        self.assertEqual(response.cookies['c']['samesite'], 'lax')
diff --git a/tests/sessions_tests/tests.py b/tests/sessions_tests/tests.py
index 24e4e0c81b..3254013d50 100644
--- a/tests/sessions_tests/tests.py
+++ b/tests/sessions_tests/tests.py
@@ -755,8 +755,9 @@ 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])
         )
@@ -787,8 +788,9 @@ 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])
         )