Network Working Group Y. Weiss
Internet-Draft Shopify
Intended status: Informational 20 March 2025
Expires: 21 September 2025
Delete-Cookie
draft-deletecookie-weiss-http-00
Abstract
This document specifies a Delete-Cookie HTTP header that instructs
clients to delete cookies of certain names, without requiring the
server to know more details about them.
About This Document
This note is to be removed before publishing as an RFC.
The latest revision of this draft can be found at
https://yoavweiss.github.io/delete-cookie/draft-deletecookie-weiss-
http.html. Status information for this document may be found at
https://datatracker.ietf.org/doc/draft-deletecookie-weiss-http/.
Source for this draft and an issue tracker can be found at
https://github.com/yoavweiss/delete-cookie.
Status of This Memo
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Copyright Notice
Copyright (c) 2025 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Notational Conventions . . . . . . . . . . . . . . . . . 3
2. Delete-Cookie . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. Example . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Security Considerations . . . . . . . . . . . . . . . . . . . 4
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
4.1. Header Field Registration . . . . . . . . . . . . . . . . 5
5. Normative References . . . . . . . . . . . . . . . . . . . . 5
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 5
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 5
1. Introduction
Long-operating web sites can often find themselves dealing with
"cookie cruft" - cookies that no longer have backend logic that
corresponds with them.
Such cookies may have been set at some point in the past with far-
reaching expiration dates, and are now causing useless cookie bloat
at best, or using up quotas at the expense of relevant cookies at
worst
Deleting cookies is possible today by setting their expiry date to
one in the past, but that requires one to know the "domain" and
"path" parameters with which the cookies were set. That is not
something that can be passively observed on the server side by
default.
This draft proposes a new Delete-Cookie header which will enable
servers to instruct clients to delete cookies of a certain name from
their cookie stores.
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1.1. Notational Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
This document uses the following terminology from Section 3 of
[STRUCTURED-FIELDS] to specify syntax and parsing: Lists, strings.
2. Delete-Cookie
The Delete-Cookie response header is a Structured Field
[STRUCTURED-FIELDS] List of strings. Each string represents a cookie
[COOKIES] name to be deleted.
A user agent that receives a Delete-Cookie response header MUST
process it before any Set-Cookie headers received as part of the same
response.
_Note:_ The relevant processing needs to happen before step 15 of the
network fetch (https://fetch.spec.whatwg.org/#http-network-fetch)
algorithm.
When receiving a Delete-Cookie response header, the user agent MUST:
1. If the response was not delivered over a "secure" connection (as
defined by the user agent) [COOKIES], return.
2. Let host be the canonicalized response URL's host name.
3. Let parsed be the result of parsing the header's value as a List,
as per [STRUCTURED-FIELDS], Section 4.2.1.
4. If parsing fails, return.
5. For each name in parsed:
1. If name is not a String [STRUCTURED-FIELDS], continue.
_Note:_ The above ignores any parameters in the header's
value List.
2. Let matching cookies be the set of cookies from the user
agent's cookie store that meet all the following
requirements:
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1. The cookie's name is name.
_Note:_ This ensures that cookies with an empty name can be
deleted using the empty string. It also ensures that
multiple cookies with the same name (and different paths,
domains or other attributes) will all be deleted.
1. Either of the following is true:
1. The cookie's host-only-flag is true, and the cookie's
domain is identical to host.
_Note:_ The ensures that a server can't delete host-only
cookies that aren't destined to its host.
1. The cookie's host-only-flag is false, and the
cookie's domain domain-matches host, as per
[COOKIES], Section 5.1.3.
3. For each cookie in matching cookies:
1. Remove cookie from the user agent's cookie store.
2.1. Example
MegaCorp servers receive a request from a client with the following
header:
Cookie: foo=bar, fizz=baz
The server operators know that cookies named "foo" and "fizz" are no
longer meaningful for their service, and are unaware when and how
those cookies were set. In order to clear that user's cookie store,
they send the following header:
Delete-Cookie: "foo", "fizz"
That clears the client's cookie store of "foo" and "fizz" and ensures
that these cookies won't be sent again.
3. Security Considerations
The Delete-Cookie header enables servers to delete cookies from user
agents on their own registrable domains. These servers could have
already deleted these same cookies by setting cookies with identical
name, path and domain with an expiration date of 0. As such the
header does not provide servers any new capabilities, beyond the
convenience of not having to know the path and domain of a cookie in
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order to delete it.
4. IANA Considerations
4.1. Header Field Registration
IANA is asked to update the "Hypertext Transfer Protocol (HTTP) Field
Name Registry" registry maintained at
<https://www.iana.org/assignments/http-fields/http-fields.xhtml>
according to the table below:
+===============+===========+============================+
| Field Name | Status | Reference |
+===============+===========+============================+
| Delete-Cookie | permanent | Section 2 of this document |
+---------------+-----------+----------------------------+
Table 1
5. Normative References
[COOKIES] "Cookies HTTP State Management Mechanism", February 2025,
<https://datatracker.ietf.org/doc/draft-ietf-httpbis-
rfc6265bis/>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/rfc/rfc2119>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/rfc/rfc8174>.
[STRUCTURED-FIELDS]
"Structured Field Values for HTTP", May 2024,
<https://datatracker.ietf.org/doc/draft-ietf-httpbis-
sfbis/>.
Acknowledgments
Thanks to Anne van Kesteren and Pat Meenan for their feedback on
early versions of this proposal.
Author's Address
Yoav Weiss
Shopify
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Email: yoav@yoav.ws
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