Privacy Pass Reverse Flow HTTP Transport
draft-meunier-privacypass-reverse-flow-http-00
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| Document | Type | Active Internet-Draft (individual) | |
|---|---|---|---|
| Author | Thibault Meunier | ||
| Last updated | 2026-06-18 | ||
| RFC stream | (None) | ||
| Intended RFC status | (None) | ||
| Formats | |||
| Stream | Stream state | (No stream defined) | |
| Consensus boilerplate | Unknown | ||
| RFC Editor Note | (None) | ||
| IESG | IESG state | I-D Exists | |
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draft-meunier-privacypass-reverse-flow-http-00
Privacy Pass T. Meunier
Internet-Draft Cloudflare Inc.
Intended status: Informational 18 June 2026
Expires: 20 December 2026
Privacy Pass Reverse Flow HTTP Transport
draft-meunier-privacypass-reverse-flow-http-00
Abstract
This document specifies an instantiation of Privacy Pass Reverse Flow
[REVERSE-FLOW] where HTTP is used as a transport mechanism.
It describes a novel HTTP header field that Clients and Origins can
use to carry reverse flow data.
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://thibmeu.github.io/draft-meunier-privacypass-reverse-flow-
informational/draft-meunier-privacypass-reverse-flow-http.html.
Status information for this document may be found at
https://datatracker.ietf.org/doc/draft-meunier-privacypass-reverse-
flow-http/.
Discussion of this document takes place on the Privacy Pass Working
Group mailing list (mailto:privacy-pass@ietf.org), which is archived
at https://mailarchive.ietf.org/arch/browse/privacy-pass/. Subscribe
at https://www.ietf.org/mailman/listinfo/privacy-pass/.
Source for this draft and an issue tracker can be found at
https://github.com/thibmeu/draft-meunier-privacypass-reverse-flow-
informational.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
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Internet-Draft Privacy Pass Reverse Flow HTTP Transport June 2026
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 20 December 2026.
Copyright Notice
Copyright (c) 2026 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document. Code Components
extracted from this document must include Revised BSD License text as
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provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. PrivacyPass-Reverse Header Field . . . . . . . . . . . . . . 3
3.1. Example . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
5. References . . . . . . . . . . . . . . . . . . . . . . . . . 4
5.1. Normative References . . . . . . . . . . . . . . . . . . 4
5.2. Informative References . . . . . . . . . . . . . . . . . 4
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 4
Changelog . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 5
1. Introduction
This document specifies an instantiation of Privacy Pass Reverse Flow
[REVERSE-FLOW] where HTTP is used as a transport mechanism.
[REVERSE-FLOW] specifies an architecture in which a client can both
present a token and initiate a new credential issuance flow.
As described in Section 4 of [REVERSE-FLOW], this requires in-band
encoding of information used by the issuance protocol.
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This document introduces a new HTTP header field as defined in
[RFC9110]. This allows Clients to convey a CredentialRequest, and
Origins to transmit a CredentialResponse.
2. Terminology
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.
3. PrivacyPass-Reverse Header Field
A Client or an Origin following [REVERSE-FLOW] MAY include a
PrivacyPass-Reverse header field to communicate Privacy Pass protocol
data. This header field contains a base64url (per [BASE64]) encoded
CredentialRequest or CredentialResponse.
+---------------+ +--------+ +--------+
| Origin Issuer | | Origin | | Client |
+--+------------+ +---+----+ +---+----+
| | |
| |<-- PrivacyPass-Reverse: CredentialRequest ---+
|<-- CredentialRequest ---+ |
+--- CredentialResponse ->| |
| +-- PrivacyPass-Reverse: CredentialResponse -->|
| | |
Figure 1: Privacy Pass with a Reverse Flow through PrivacyPass-
Reverse header field
3.1. Example
Below is an example request that uses [RFC9577] to pass the request
Token, as well as PrivacyPass-Reverse for its reverse flow.
GET /foo HTTP/1.1
Host: example.com
Authorization: PrivateToken token="abc..."
PrivacyPass-Reverse: "def..."
HTTP/1.1 200 OK
PrivacyPass-Reverse: "001..."
[BODY]
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4. IANA Considerations
This document has no IANA actions.
5. References
5.1. Normative References
[BASE64] Josefsson, S., "The Base16, Base32, and Base64 Data
Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006,
<https://www.rfc-editor.org/rfc/rfc4648>.
[REVERSE-FLOW]
Meunier, T., "Privacy Pass Reverse Flow", Work in
Progress, Internet-Draft, draft-meunier-privacypass-
reverse-flow-04, 13 May 2026,
<https://datatracker.ietf.org/doc/html/draft-meunier-
privacypass-reverse-flow-04>.
[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>.
5.2. Informative References
[RFC9110] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
Ed., "HTTP Semantics", STD 97, RFC 9110,
DOI 10.17487/RFC9110, June 2022,
<https://www.rfc-editor.org/rfc/rfc9110>.
[RFC9577] Pauly, T., Valdez, S., and C. A. Wood, "The Privacy Pass
HTTP Authentication Scheme", RFC 9577,
DOI 10.17487/RFC9577, June 2024,
<https://www.rfc-editor.org/rfc/rfc9577>.
Acknowledgments
TODO
Changelog
v00
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* Initial draft
Author's Address
Thibault Meunier
Cloudflare Inc.
Email: ot-ietf@thibault.uk
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