[3.1.x] 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.
Backport of 240cbb63bf9965c63d7a3cc9032f91410f414d46 from master

10 files changed, 66 insertions, 10 deletions

diff --git a/django/contrib/messages/storage/cookie.py b/django/contrib/messages/storage/cookie.py
index 78256ca3b2..b51e292aa0 100644
--- a/django/contrib/messages/storage/cookie.py
+++ b/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):
         """
diff --git a/django/contrib/sessions/middleware.py b/django/contrib/sessions/middleware.py
index 63013eef7a..95ad30ce7f 100644
--- a/django/contrib/sessions/middleware.py
+++ b/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:
diff --git a/django/http/response.py b/django/http/response.py
index e00bcacefb..c0ed93c44e 100644
--- a/django/http/response.py
+++ b/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
diff --git a/docs/ref/request-response.txt b/docs/ref/request-response.txt
index 3c63af5978..86a55bc45d 100644
--- a/docs/ref/request-response.txt
+++ b/docs/ref/request-response.txt
@@ -902,7 +902,7 @@ 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.
@@ -911,6 +911,10 @@ 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..9bd2246b44
--- /dev/null
+++ b/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`).
diff --git a/docs/releases/3.0.9.txt b/docs/releases/3.0.9.txt
index adc0f30b10..08e16a681f 100644
--- a/docs/releases/3.0.9.txt
+++ b/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`).
diff --git a/docs/releases/index.txt b/docs/releases/index.txt
index 1d9c4fe635..3bc80ccd2e 100644
--- a/docs/releases/index.txt
+++ b/docs/releases/index.txt
@@ -48,6 +48,7 @@ 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 5675cd15eb..f1428fdf32 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 a52443eefe..c7c35219b2 100644
--- a/tests/responses/test_cookie.py
+++ b/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')
diff --git a/tests/sessions_tests/tests.py b/tests/sessions_tests/tests.py
index 6c6d7dd3f2..248dae82aa 100644
--- a/tests/sessions_tests/tests.py
+++ b/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])
         )