Fixed #28989 -- Fixed HttpResponse.delete_cookie() for cookies that use __Secure/Host prefixes.

django/http/response.py

@@ -205,8 +205,13 @@ class HttpResponseBase:
         return self.set_cookie(key, value, **kwargs)
 
     def delete_cookie(self, key, path='/', domain=None):
-        self.set_cookie(key, max_age=0, path=path, domain=domain,
+        # Most browsers ignore the Set-Cookie header if the cookie name starts
-                        expires='Thu, 01 Jan 1970 00:00:00 GMT')
+        # 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',
+        )
 
     # Common methods used by subclasses
 

tests/responses/test_cookie.py

@@ -91,3 +91,16 @@ class DeleteCookieTests(SimpleTestCase):
         self.assertEqual(cookie['path'], '/')
         self.assertEqual(cookie['secure'], '')
         self.assertEqual(cookie['domain'], '')
+
+    def test_delete_cookie_secure_prefix(self):
+        """
+        delete_cookie() sets the secure flag if the cookie name starts with
+        __Host- or __Secure- (without that, browsers ignore cookies with those
+        prefixes).
+        """
+        response = HttpResponse()
+        for prefix in ('Secure', 'Host'):
+            with self.subTest(prefix=prefix):
+                cookie_name = '__%s-c' % prefix
+                response.delete_cookie(cookie_name)
+                self.assertEqual(response.cookies[cookie_name]['secure'], True)