Using TLS Application-Layer Protocol Settings (ALPS) in HTTP
draft-vvv-httpbis-alps-01
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Victor Vasiliev
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2021-01-21
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HTTP Working Group V. Vasiliev
Internet-Draft Google
Intended status: Standards Track 21 January 2021
Expires: 25 July 2021
Using TLS Application-Layer Protocol Settings (ALPS) in HTTP
draft-vvv-httpbis-alps-01
Abstract
This document describes the use of TLS Application-Level Protocol
Settings (ALPS) in HTTP/2 and HTTP/3. Additionally, it defines a set
of additional HTTP SETTINGS parameters that would normally be
impractical without ALPS.
Discussion Venues
This note is to be removed before publishing as an RFC.
Discussion of this document takes place on the HTTPBIS Working Group
mailing list (httpbis@ietf.org), which is archived at
https://mailarchive.ietf.org/arch/browse/httpbis/
(https://mailarchive.ietf.org/arch/browse/httpbis/).
Source for this draft and an issue tracker can be found at
https://github.com/vasilvv/httpbis-alps (https://github.com/vasilvv/
httpbis-alps).
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/.
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 25 July 2021.
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Copyright Notice
Copyright (c) 2021 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
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions and Definitions . . . . . . . . . . . . . . . . . 3
3. Use of ALPS in HTTP . . . . . . . . . . . . . . . . . . . . . 3
4. Security Considerations . . . . . . . . . . . . . . . . . . . 3
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
6. Normative References . . . . . . . . . . . . . . . . . . . . 4
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 4
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 4
1. Introduction
HTTP/2 defines a mechanism for exchanging the protocol settings using
a SETTINGS frame ([RFC7540], Section 6.5). HTTP/3 uses a similar
mechanism ([HTTP3], Section 7.2.4). One of the properties of the
mechanism as defined by both of those protocols is that the parties
start out without having access to the entirety of the peer's
settings. This means that they have to initially operate using the
default settings, and after receiving the SETTINGS frame, they have
to find a way to transition from the default to the exchanged
settings.
HTTP is commonly used in conjunction with TLS. TLS performs its own
handshake that precedes any data being exchanged by the HTTP layer
itself. The TLS Application-Level Protocol Settings extension [ALPS]
allows settings negotiation to be performed within the TLS handshake,
thus making the result immediately available to the HTTP layer as
soon as the handshake completes. This removes the need for
synchronizing settings, and makes them available earlier than they
would be otherwise.
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This document defines how ALPS is used with HTTP/2 and HTTP/3, and
introduces certain new settings that would not be practical without
ALPS.
2. Conventions and Definitions
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. Use of ALPS in HTTP
If ALPS is successfully negotiated during the TLS handshake for an
HTTP/2 connection, the ALPS payload for both peers SHALL be a
sequence of HTTP/2 frames. Frames SHALL NOT be present in ALPS
unless they are explicitly allowed to be there; this document only
allows the SETTINGS frame ([RFC7540], Section 6.5.1). Sending a
SETTINGS frame in ALPS supersedes the requirement to send a SETTINGS
frame at the beginning of the connection. All settings exchanged via
ALPS SHALL be automatically treated as acknowledged.
If ALPS is successfully negotiated during TLS handshake for an HTTP/3
connection, the ALPS payload for both peers SHALL be a sequence of
HTTP/3 frames. Frames SHALL NOT be present in ALPS unless they are
explicitly allowed to be there; this document only allows the
SETTINGS frame ([HTTP3], Section 7.2.4). Sending a SETTINGS frame in
ALPS supersedes the requirement to send a SETTINGS frame at the
beginning of the control stream.
Since settings exchanged through ALPS are always available at the
beginning of the connection, some HTTP extensions may opt to require
those to be sent through ALPS. Such extensions are exempt from the
initialization requirements of the Section 7.2.4.2 of [HTTP3].
4. Security Considerations
In ALPS, both client and server settings are sent encrypted.
Settings communicated through ALPS are presented to all clients
before they are authenticated; thus, if a server relies on TLS client
authentication and considers its settings private, it MUST NOT use
the mechanism defined in this document.
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5. IANA Considerations
IANA will add an "Allowed in ALPS" column to the "HTTP/2 Frames"
section of the "Hypertext Transfer Protocol version 2 (HTTP/2)
Parameters" registry, with a value set to "Yes" for SETTINGS (0x4),
and to "No" for all other previously defined settings.
TODO: Add HTTP/3 once IANA has an HTTP/3 registry.
6. Normative References
[ALPS] Vasiliev, V., "TLS Application-Layer Protocol Settings
Extension", Work in Progress, Internet-Draft, draft-vvv-
tls-alps-latest,
<https://tools.ietf.org/html/draft-vvv-tls-alps-latest>.
[HTTP3] Bishop, M., Ed., "Hypertext Transfer Protocol Version 3
(HTTP/3)", Work in Progress, Internet-Draft, draft-ietf-
quic-http-latest,
<https://tools.ietf.org/html/draft-ietf-quic-http-latest>.
[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/info/rfc2119>.
[RFC7540] Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext
Transfer Protocol Version 2 (HTTP/2)", RFC 7540,
DOI 10.17487/RFC7540, May 2015,
<https://www.rfc-editor.org/info/rfc7540>.
[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/info/rfc8174>.
Acknowledgments
This document has benefited from contributions and suggestions from
David Benjamin, Nick Harper, David Schinazi, and many others.
Author's Address
Victor Vasiliev
Google
Email: vasilvv@google.com
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