HTTP Unprompted Authentication
draft-ietf-httpbis-unprompted-auth-00
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| Last updated | 2023-02-24 | ||
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draft-ietf-httpbis-unprompted-auth-00
HTTPBIS D. Schinazi
Internet-Draft Google LLC
Intended status: Standards Track D. Oliver
Expires: 28 August 2023 Guardian Project
J. Hoyland
Cloudflare Inc.
24 February 2023
HTTP Unprompted Authentication
draft-ietf-httpbis-unprompted-auth-00
Abstract
Existing HTTP authentication mechanisms are probeable in the sense
that it is possible for an unauthenticated client to probe whether an
origin serves resources that require authentication. It is possible
for an origin to hide the fact that it requires authentication by not
generating Unauthorized status codes, however that only works with
non-cryptographic authentication schemes: cryptographic schemes (such
as signatures or message authentication codes) require a fresh nonce
to be signed, and there is no existing way for the origin to share
such a nonce without exposing the fact that it serves resources that
require authentication. This document proposes a new non-probeable
cryptographic authentication scheme.
About This Document
This note is to be removed before publishing as an RFC.
Status information for this document may be found at
https://datatracker.ietf.org/doc/draft-ietf-httpbis-unprompted-auth/.
Discussion of this document takes place on the HTTP Working Group
mailing list (mailto:ietf-http-wg@w3.org), which is archived at
https://lists.w3.org/Archives/Public/ietf-http-wg/. Working Group
information can be found at https://httpwg.org/.
Source for this draft and an issue tracker can be found at
https://github.com/httpwg/http-extensions/labels/unprompted-auth.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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Copyright Notice
Copyright (c) 2023 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/
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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Conventions and Definitions . . . . . . . . . . . . . . . 3
2. Computing the Authentication Proof . . . . . . . . . . . . . 3
3. Header Field Definition . . . . . . . . . . . . . . . . . . . 4
4. Authentication Parameters . . . . . . . . . . . . . . . . . . 4
4.1. The u Parameter . . . . . . . . . . . . . . . . . . . . . 4
4.2. The p Parameter . . . . . . . . . . . . . . . . . . . . . 4
4.3. The s Parameter . . . . . . . . . . . . . . . . . . . . . 4
4.4. The h Parameter . . . . . . . . . . . . . . . . . . . . . 4
5. Authentication Schemes . . . . . . . . . . . . . . . . . . . 5
5.1. Signature . . . . . . . . . . . . . . . . . . . . . . . . 5
5.2. HMAC . . . . . . . . . . . . . . . . . . . . . . . . . . 5
5.3. Other HTTP Authentication Schemes . . . . . . . . . . . . 6
6. Intermediary Considerations . . . . . . . . . . . . . . . . . 6
7. Security Considerations . . . . . . . . . . . . . . . . . . . 6
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
8.1. Unprompted-Authentication Header Field . . . . . . . . . 6
8.2. HTTP Authentication Schemes Registry . . . . . . . . . . 7
8.3. TLS Keying Material Exporter Labels . . . . . . . . . . . 7
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
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9.1. Normative References . . . . . . . . . . . . . . . . . . 7
9.2. Informative References . . . . . . . . . . . . . . . . . 8
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction
Existing HTTP authentication mechanisms (see Section 11 of [HTTP])
are probeable in the sense that it is possible for an unauthenticated
client to probe whether an origin serves resources that require
authentication. It is possible for an origin to hide the fact that
it requires authentication by not generating Unauthorized status
codes, however that only works with non-cryptographic authentication
schemes: cryptographic schemes (such as signatures or message
authentication codes) require a fresh nonce to be signed, and there
is no existing way for the origin to share such a nonce without
exposing the fact that it serves resources that require
authentication. This document proposes a new non-probeable
cryptographic authentication scheme.
There are scenarios where servers may want to expose the fact that
authentication is required for access to specific resources. This is
left for future work.
1.1. 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.
This document uses the following terminology from Section 3 of
[STRUCTURED-FIELDS] to specify syntax and parsing: Integer and Byte
Sequence.
2. Computing the Authentication Proof
This document only defines the Signature and HMAC authentication
schemes for uses of HTTP with TLS [TLS]. This includes any use of
HTTP over TLS as typically used for HTTP/2 [HTTP/2], or HTTP/3
[HTTP/3] where the transport protocol uses TLS as its authentication
and key exchange mechanism [QUIC-TLS].
The user agent leverages a TLS keying material exporter [KEY-EXPORT]
to generate a nonce which can be signed using the user's key. The
keying material exporter uses a label that starts with the characters
"EXPORTER-HTTP-Unprompted-Authentication-" (see Section 5 for the
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labels and contexts used by each scheme). The TLS keying material
exporter is used to generate a 32-byte key which is then used as a
nonce.
3. Header Field Definition
The "Unprompted-Authentication" header field allows a user agent to
authenticate with an origin server. The authentication is scoped to
the HTTP request associated with this header field. The value of the
Unprompted-Authentication header field is a credentials object, as
defined in Section 11.4 of [HTTP]. Credentials contain an
authentication scheme followed by optional authentication parameters.
4. Authentication Parameters
This specification defines the following authentication parameters,
they can be used by the authentication schemes defined in Section 5.
4.1. The u Parameter
The OPTIONAL "u" (user ID) parameter is a byte sequence that
specifies the user ID that the user agent wishes to authenticate.
4.2. The p Parameter
The OPTIONAL "p" (proof) parameter is a byte sequence that specifies
the proof that the user agent provides to attest to possessing the
credential that matches its user ID.
4.3. The s Parameter
The OPTIONAL "s" (signature) parameter is an integer that specifies
the signature algorithm used to compute the proof transmitted in the
"p" directive. Its value is an integer between 0 and 255 inclusive
from the IANA "TLS SignatureAlgorithm" registry maintained at
<https://www.iana.org/assignments/tls-parameters#tls-parameters-16>.
4.4. The h Parameter
The OPTIONAL "h" (hash) parameter is an integer that specifies the
hash algorithm used to compute the proof transmitted in the "p"
directive. Its value is an integer between 0 and 255 inclusive from
the IANA "TLS HashAlgorithm" registry maintained at
<https://www.iana.org/assignments/tls-parameters#tls-parameters-18>.
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5. Authentication Schemes
This document defines the "Signature" and "HMAC" HTTP authentication
schemes.
5.1. Signature
The "Signature" HTTP Authentication Scheme uses asymmetric
cyptography. User agents possess a user ID and a public/private key
pair, and origin servers maintain a mapping of authorized user IDs to
their associated public keys. When using this scheme, the "u", "p",
and "s" parameters are REQUIRED. The TLS keying material export
label for this scheme is "EXPORTER-HTTP-Unprompted-Authentication-
Signature" and the associated context is empty. The nonce is then
signed using the selected asymmetric signature algorithm and
transmitted as the proof directive.
For example, the user ID "john.doe" authenticating using Ed25519
[ED25519] could produce the following header field (lines are folded
to fit):
Unprompted-Authentication: Signature u=:am9obi5kb2U=:;s=7;
p=:SW5zZXJ0IHNpZ25hdHVyZSBvZiBub25jZSBoZXJlIHdo
aWNoIHRha2VzIDUxMiBiaXRzIGZvciBFZDI1NTE5IQ==:
5.2. HMAC
The "HMAC" HTTP Authentication Scheme uses symmetric cyptography.
User agents possess a user ID and a secret key, and origin servers
maintain a mapping of authorized user IDs to their associated secret
key. When using this scheme, the "u", "p", and "h" parameters are
REQUIRED. The TLS keying material export label for this scheme is
"EXPORTER-HTTP-Unprompted-Authentication-HMAC" and the associated
context is empty. The nonce is then HMACed using the selected HMAC
algorithm and transmitted as the proof directive.
For example, the user ID "john.doe" authenticating using HMAC-SHA-512
[SHA] could produce the following header field (lines are folded to
fit):
Unprompted-Authentication: HMAC u="am9obi5kb2U=";h=6;
p="SW5zZXJ0IEhNQUMgb2Ygbm9uY2UgaGVyZSB3aGljaCB0YWtl
cyA1MTIgYml0cyBmb3IgU0hBLTUxMiEhISEhIQ=="
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5.3. Other HTTP Authentication Schemes
The HTTP Authentication Scheme registry maintained by IANA at
<https://www.iana.org/assignments/http-authschemes/http-
authschemes.xhtml> contains entries not defined in this document.
Those entries MAY be used with Unprompted Authentication.
6. Intermediary Considerations
Since the Signature and HMAC HTTP Authentication Schemes leverage TLS
keying material exporters, their output cannot be transparently
forwarded by HTTP intermediaries. HTTP intermediaries that support
this specification will validate the authentication received from the
client themselves, then inform the upstream HTTP server of the
presence of valid authentication using some other mechanism.
7. Security Considerations
Unprompted Authentication allows a user-agent to authenticate to an
origin server while guaranteeing freshness and without the need for
the server to transmit a nonce to the user agent. This allows the
server to accept authenticated clients without revealing that it
supports or expects authentication for some resources. It also
allows authentication without the user agent leaking the presence of
authentication to observers due to clear-text TLS Client Hello
extensions.
The authentication proofs described in this document are not bound to
individual HTTP requests; if the same user sends an authentication
proof on multiple requests they will all be identical. This allows
for better compression when sending over the wire, but implies that
client implementations that multiplex different security contexts
over a single HTTP connection need to ensure that those contexts
cannot read each other's header fields. Otherwise, one context would
be able to replay the unprompted authentication header field of
another. This constraint is met by modern Web browsers. If an
attacker were to compromise the browser such that it could access
another context's memory, the attacker might also be able to access
the corresponding key, so binding authentication to requests would
not provide much benefit in practice.
8. IANA Considerations
8.1. Unprompted-Authentication Header Field
This document will request IANA to register the following entry in
the "HTTP Field Name" registry maintained at
<https://www.iana.org/assignments/http-fields>:
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Field Name: Unprompted-Authentication
Template: None
Status: provisional (permanent if this document is approved)
Reference: This document
Comments: None
8.2. HTTP Authentication Schemes Registry
This document, if approved, requests IANA to add two new entries to
the "HTTP Authentication Schemes" Registry maintained at
<https://www.iana.org/assignments/http-authschemes>. Both entries
have the Reference set to this document, and the Notes empty. The
Authentication Scheme Name of the entries are:
* Signature
* HMAC
8.3. TLS Keying Material Exporter Labels
This document, if approved, requests IANA to register the following
entries in the "TLS Exporter Labels" registry maintained at
<https://www.iana.org/assignments/tls-parameters#exporter-labels>:
* EXPORTER-HTTP-Unprompted-Authentication-Signature
* EXPORTER-HTTP-Unprompted-Authentication-HMAC
Both of these entries are listed with the following qualifiers:
DTLS-OK: N
Recommended: Y
Reference: This document
9. References
9.1. Normative References
[HTTP] 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>.
[KEY-EXPORT]
Rescorla, E., "Keying Material Exporters for Transport
Layer Security (TLS)", RFC 5705, DOI 10.17487/RFC5705,
March 2010, <https://www.rfc-editor.org/rfc/rfc5705>.
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[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]
Nottingham, M. and P-H. Kamp, "Structured Field Values for
HTTP", RFC 8941, DOI 10.17487/RFC8941, February 2021,
<https://www.rfc-editor.org/rfc/rfc8941>.
[TLS] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
<https://www.rfc-editor.org/rfc/rfc8446>.
9.2. Informative References
[ED25519] Josefsson, S. and J. Schaad, "Algorithm Identifiers for
Ed25519, Ed448, X25519, and X448 for Use in the Internet
X.509 Public Key Infrastructure", RFC 8410,
DOI 10.17487/RFC8410, August 2018,
<https://www.rfc-editor.org/rfc/rfc8410>.
[HTTP/2] Thomson, M., Ed. and C. Benfield, Ed., "HTTP/2", RFC 9113,
DOI 10.17487/RFC9113, June 2022,
<https://www.rfc-editor.org/rfc/rfc9113>.
[HTTP/3] Bishop, M., Ed., "HTTP/3", RFC 9114, DOI 10.17487/RFC9114,
June 2022, <https://www.rfc-editor.org/rfc/rfc9114>.
[QUIC-TLS] Thomson, M., Ed. and S. Turner, Ed., "Using TLS to Secure
QUIC", RFC 9001, DOI 10.17487/RFC9001, May 2021,
<https://www.rfc-editor.org/rfc/rfc9001>.
[SHA] Eastlake 3rd, D. and T. Hansen, "US Secure Hash Algorithms
(SHA and SHA-based HMAC and HKDF)", RFC 6234,
DOI 10.17487/RFC6234, May 2011,
<https://www.rfc-editor.org/rfc/rfc6234>.
Acknowledgments
The authors would like to thank many members of the IETF community,
as this document is the fruit of many hallway conversations. Ben
Schwartz contributed ideas to this document.
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Authors' Addresses
David Schinazi
Google LLC
1600 Amphitheatre Parkway
Mountain View, CA 94043
United States of America
Email: dschinazi.ietf@gmail.com
David M. Oliver
Guardian Project
Email: david@guardianproject.info
URI: https://guardianproject.info
Jonathan Hoyland
Cloudflare Inc.
Email: jonathan.hoyland@gmail.com
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