Support Cookie CHIPS

CHIPS, Cookies Having Independent Partitioned State, allows for
cookies to be opted into partitioned storage which is especially
useful for thrid party cookies.

CHANGES.rst

@@ -1,5 +1,13 @@
 .. currentmodule:: werkzeug
 
+Version 3.1.0
+-------------
+
+Unreleased
+
+-  Support Cookie CHIPS (Partitioned Cookies). :issue:`2797`
+
+
 Version 3.0.1
 -------------
 

src/werkzeug/http.py

@@ -1216,6 +1216,7 @@ def dump_cookie(
     sync_expires: bool = True,
     max_size: int = 4093,
     samesite: str | None = None,
+    partitioned: bool = False,
 ) -> str:
     """Create a Set-Cookie header without the ``Set-Cookie`` prefix.
 
@@ -1252,9 +1253,13 @@ def dump_cookie(
         <cookie_>`_. Set to 0 to disable this check.
     :param samesite: Limits the scope of the cookie such that it will
         only be attached to requests if those requests are same-site.
+    :param partitioned: Opts the cookie into partitioned storage.
 
     .. _`cookie`: http://browsercookielimits.squawky.net/
 
+    .. versionchanged:: 3.1
+        The ``partitioned`` parameter was added.
+
     .. versionchanged:: 3.0
         Passing bytes, and the ``charset`` parameter, were removed.
 
@@ -1298,6 +1303,9 @@ def dump_cookie(
         if samesite not in {"Strict", "Lax", "None"}:
             raise ValueError("SameSite must be 'Strict', 'Lax', or 'None'.")
 
+    if partitioned and not secure:
+        raise ValueError("Patitioned cookies must also be secure")
+
     # Quote value if it contains characters not allowed by RFC 6265. Slash-escape with
     # three octal digits, which matches http.cookies, although the RFC suggests base64.
     if not _cookie_no_quote_re.fullmatch(value):
@@ -1319,6 +1327,7 @@ def dump_cookie(
         ("HttpOnly", httponly),
         ("Path", path),
         ("SameSite", samesite),
+        ("Partitioned", partitioned),
     ):
         if v is None or v is False:
             continue

tests/test_http.py

@@ -576,6 +576,14 @@ def test_cookie_samesite_invalid(self):
         with pytest.raises(ValueError):
             http.dump_cookie("foo", "bar", samesite="invalid")
 
+    def test_cookie_partitioned(self):
+        value = http.dump_cookie("foo", "bar", partitioned=True, secure=True)
+        assert value == "foo=bar; Secure; Path=/; Partitioned"
+
+    def test_cookie_partitioned_invalid(self):
+        with pytest.raises(ValueError):
+            http.dump_cookie("foo", "bar", partitioned=True, secure=False)
+
 
 class TestRange:
     def test_if_range_parsing(self):