HTTP Transport Authentication

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Table of Contents

1. Introduction

The most common existing authentication mechanisms for HTTP are sent with each HTTP request, and authenticate that request instead of the underlying HTTP connection, or transport. While these mechanisms work well for existing uses of HTTP, they are not suitable for emerging applications that multiplex non-HTTP traffic inside an HTTP connection. This document describes the HTTP Transport Authentication Framework, a method of authenticating not only an HTTP request, but also its underlying transport.¶

Traditional HTTP semantics specify that HTTP is a stateless protocol where each request can be understood in isolation [RFC7230]. However, the emergence of QUIC [QUIC] as a new transport protocol that can carry HTTP [HTTP3] and the existence of QUIC extensions such as the DATAGRAM frame [DGRAM] enable new uses of HTTP such as [WEBTRANS-H] and [MASQUE] where some traffic is exchanged that is disctinct from HTTP requests and responses. In order to authenticate this traffic, it is necessary to authenticate the underlying transport (e.g., QUIC or TLS [RFC8446]) instead of authenticate each request individually. This mechanism aims to supplement the HTTP Authentication Framework [RFC7235], not replace it.¶

Note that there is currently no mechanism for origin servers to request that user agents authenticate themselves using Transport Authentication, this is left as future work.¶

  OWS           = <OWS, see {{RFC7230}}, Section 3.2.3>
  quoted-string = <quoted-string, see {{RFC7230}}, Section 3.2.6>
  token         = <token, see {{RFC7230}}, Section 3.2.6>
  token68       = <token, see {{RFC7235}}, Section 2.1>
  oid           = <oid, see {{RFC3061}}, Section 2>

2. Computing the Authentication Proof

This document only defines Transport Authentication for uses of HTTP with TLS. This includes any use of HTTP over TLS as typically used for HTTP/2, or 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 [RFC5705] to generate a nonce which can be signed using the user-id's key. The keying material exporter uses a label that starts with the characters "EXPORTER-HTTP-Transport-Authentication-" (see Section 4 for the 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 "Transport-Authentication" header allows a user agent to authenticate its transport connection with an origin server.¶

  Transport-Authentication = tpauth-scheme *( OWS ";" OWS param )
  tpauth-scheme            = token
  param                    = token "=" ( token / quoted-string )

    u = token68

    p = token68

    a = oid

4. Transport Authentication Schemes

The Transport Authentication Framework allows defining Transport Authentication Schemes, which specify how to authenticate user-ids. This documents defined the "Signature" and "HMAC" schemes.¶

Transport-Authentication: Signature u="am9obi5kb2U=";
a=1.3.101.112;
p="SW5zZXJ0IHNpZ25hdHVyZSBvZiBub25jZSBoZXJlIHdo
aWNoIHRha2VzIDUxMiBiaXRzIGZvciBFZDI1NTE5IQ=="

Transport-Authentication: HMAC u="am9obi5kb2U=";
a=2.16.840.1.101.3.4.2.3;
p="SW5zZXJ0IEhNQUMgb2Ygbm9uY2UgaGVyZSB3aGljaCB0YWtl
cyA1MTIgYml0cyBmb3IgU0hBLTUxMiEhISEhIQ=="

5. Proxy Considerations

Since Transport Authentication authenticates the underlying transport by leveraging TLS keying material exporters, it cannot be transparently forwarded by proxies that terminate TLS. However it can be sent over proxied connections when TLS is performed end-to-end (e.g., when using HTTP CONNECT proxies).¶

6. Security Considerations

Transport 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.¶

7. IANA Considerations

  +--------------------------+----------+--------+---------------+
  |    Header Field Name     | Protocol | Status |   Reference   |
  +--------------------------+----------+--------+---------------+
  | Transport-Authentication |   http   |  exp   | This document |
  +--------------------------+----------+--------+---------------+

  +---------------------------------+---------------+
  | Transport Authentication Scheme |   Reference   |
  +---------------------------------+---------------+
  |            Signature            | This document |
  +---------------------------------+---------------+
  |              HMAC               | This document |
  +---------------------------------+---------------+

  +--------------------------------------------------+
  |                       Value                      |
  +--------------------------------------------------+
  | EXPORTER-HTTP-Transport-Authentication-Signature |
  +--------------------------------------------------+
  | EXPORTER-HTTP-Transport-Authentication-HMAC      |
  +--------------------------------------------------+

  +---------+-------------+---------------+
  | DTLS-OK | Recommended |   Reference   |
  +---------+-------------+---------------+
  |    N    |      Y      | This document |
  +---------+-------------+---------------+

Acknowledgments

The authors would like to thank many members of the IETF community, as this document is the fruit of many hallway conversations. Using the OID for the signature and HMAC algorithms was inspired by Signature Authentication in IKEv2 [RFC7427].¶

Author's Address