TLS Flag - Request mTLS
draft-jhoyla-req-mtls-flag-01

Network Working Group                                         J. Hoyland
Internet-Draft                                                Cloudflare
Intended status: Informational                              October 2023
Expires: 3 May 2024

                        TLS Flag - Request mTLS
                     draft-jhoyla-req-mtls-flag-01

Abstract

   Normally in TLS there is no way for the client to signal to the
   server that it has been configured with a certificate suitable for
   mTLS.  This document defines a TLS Flag [I-D.ietf-tls-tlsflags] that
   enables clients to provide this hint.

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://jhoyla.github.io/draft-jhoyla-req-mtls-flag/draft-jhoyla-req-
   mtls-flag.html.  Status information for this document may be found at
   https://datatracker.ietf.org/doc/draft-jhoyla-req-mtls-flag/.

   Source for this draft and an issue tracker can be found at
   https://github.com/jhoyla/draft-jhoyla-req-mtls-flag.

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 3 April 2024.

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RFC 0                    TLS Flag - Request mTLS            October 2023

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/
   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
   described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions and Definitions . . . . . . . . . . . . . . . . .   2
   3.  Flag specification  . . . . . . . . . . . . . . . . . . . . .   3
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   3
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   3
   6.  Normative References  . . . . . . . . . . . . . . . . . . . .   3
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .   4
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   4

1.  Introduction

   This document specifies a TLS Flag that indicates to the server that
   the client supports mTLS.  Sometimes a server does not want to
   negotiate mTLS with every client, but might wish to authenticate a
   subset of them.  In TLS 1.3 this may be done with post-handshake
   auth, however this adds an extra round-trip, and requires negotiation
   at the application layer.  A client sending the request mTLS flag in
   the ClientHello allows the server to request authentication during
   the initial handshake only when it receives a hint the client
   supports it.  This enables a number of use cases, for example
   allowing bots to authenticate themselves when mixed in with general
   traffic.

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.

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3.  Flag specification

   A server receiving this flag MAY send a CertificateRequest message.

4.  Security Considerations

   This flag should have no effect on the security of TLS, as the server
   may always send a CertificateRequest message during the handshake.
   This flag merely provides a hint that the client will be able to
   fulfil the request.  If the client sets this flag but then fails to
   provide a certificate the server MAY terminate the connection with a
   bad_certificate error.

5.  IANA Considerations

   This document requests IANA to add an entry to the TLS Flags registry
   in the TLS namespace with the following values:

   *  Value shall be TBD

   *  Flag Name shall be request_mtls.

   *  Message shall be CH

   *  Recommended shall be set to no (N)

   *  The reference shall be this document {!draft-jhoyla-req-mtls}

6.  Normative References

   [I-D.ietf-tls-tlsflags]
              Nir, Y., "A Flags Extension for TLS 1.3", Work in
              Progress, Internet-Draft, draft-ietf-tls-tlsflags-12, 23
              July 2023, <https://datatracker.ietf.org/doc/html/draft-
              ietf-tls-tlsflags-12>.

   [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>.

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Acknowledgments

   TODO acknowledge.

Author's Address

   Jonathan Hoyland
   Cloudflare
   Email: jonathan.hoyland@gmail.com

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