The "secret-token" URI Scheme

Internet Engineering Task Force (IETF)                     M. Nottingham
Request for Comments: 8959                                  January 2021
Category: Informational
ISSN: 2070-1721


                     The "secret-token" URI Scheme

Abstract

   This document registers the "secret-token" URI scheme to aid in the
   identification of authentication tokens.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for informational purposes.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Not all documents
   approved by the IESG are candidates for any level of Internet
   Standard; see Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc8959.

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Table of Contents

   1.  Introduction
     1.1.  Notational Conventions
   2.  The "secret-token" URI Scheme
   3.  IANA Considerations
   4.  Security Considerations
   5.  References
     5.1.  Normative References
     5.2.  Informative References
   Acknowledgements
   Author's Address

1.  Introduction

   It has become increasingly common to use bearer tokens as an
   authentication mechanism in various protocols.

   A bearer token is a security token with the property that any party
   in possession of the token (a "bearer") can use the token in any way
   that any other party in possession of it can.  Using a bearer token
   does not require a bearer to prove possession of cryptographic key
   material (proof-of-possession).

   Unfortunately, the number of security incidents involving accidental
   disclosure of these tokens has also increased.  For example, we now
   regularly hear about a developer committing an access token to a
   public source code repository, either because they didn't realize it
   was included in the committed code or because they didn't realize the
   implications of its disclosure.

   This specification registers the "secret-token" URI scheme to aid
   prevention of such accidental disclosures.  When tokens are easier to
   unambiguously identify, they can trigger warnings in continuous
   integration systems or be used in source code repositories
   themselves.  They can also be scanned for separately.

   For example, if cloud.example.net issues access tokens to its clients
   for later use, and it does so by formatting them as "secret-token"
   URIs, tokens that "leak" into places that they don't belong are
   easier to identify.  This could be through a variety of mechanisms;
   for example, if repo.example.com can be configured to refuse commits
   containing "secret-token" URIs, it helps its customers avoid
   accidental disclosures.

   "secret-token" URIs are intended to aid in identification of
   generated secrets, like API keys and similar tokens.  They are not
   intended for use in controlled situations where ephemeral tokens are
   used, such as things like Cross-Site Request Forgery (CSRF) tokens.

1.1.  Notational Conventions

   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 ABNF [RFC5234].  It also uses the pchar rule from
   [RFC3986].

2.  The "secret-token" URI Scheme

   The "secret-token" URI scheme identifies a token that is intended to
   be a secret.

   secret-token-URI    = secret-token-scheme ":" token
   secret-token-scheme = "secret-token"
   token               = 1*pchar

   See [RFC3986], Section 3.3 for a definition of pchar.  Disallowed
   characters -- including non-ASCII characters -- MUST be encoded into
   UTF-8 [RFC3629] and then percent-encoded ([RFC3986], Section 2.1).

   When a token is both generated and presented for authentication, the
   entire URI MUST be used, without changes.

   For example, given the URI:

   secret-token:E92FB7EB-D882-47A4-A265-A0B6135DC842%20foo

   This (character-for-character, case-sensitive) string will both be
   issued by the token authority and required for later access.
   Therefore, if the example above were used as a bearer token in
   [RFC6750], a client might send:

   GET /authenticated/stuff HTTP/1.1
   Host: www.example.com
   Authorization: Bearer
     secret-token:E92FB7EB-D882-47A4-A265-A0B6135DC842%20foo

3.  IANA Considerations

   This document registers the following value in the "Uniform Resource
   Identifier (URI) Schemes" registry:

   Scheme name:  secret-token
   Status:  provisional
   Applications/protocols that use this scheme:  none yet
   Contact:  iesg@iesg.org
   Change Controller:  IESG
   References:  RFC 8959

4.  Security Considerations

   The token ABNF rule allows tokens as small as one character.  This is
   not recommended practice; applications should evaluate their
   requirements for entropy and issue tokens correspondingly.  See
   [RFC4086] for more information.

   This URI scheme is intended to reduce the incidence of accidental
   disclosure; it cannot prevent intentional disclosure.

   If it is difficult to correctly handle secret material, or unclear as
   to what the appropriate handling is, users might choose to obfuscate
   their secret tokens in order to evade detection (for example,
   removing the URI scheme for storage).  Mitigating this risk is often
   beyond the reach of the system using the "secret-token" URI; users
   can be cautioned against such practices and be provided tools to
   help.

5.  References

5.1.  Normative References

   [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>.

   [RFC3629]  Yergeau, F., "UTF-8, a transformation format of ISO
              10646", STD 63, RFC 3629, DOI 10.17487/RFC3629, November
              2003, <https://www.rfc-editor.org/info/rfc3629>.

   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66,
              RFC 3986, DOI 10.17487/RFC3986, January 2005,
              <https://www.rfc-editor.org/info/rfc3986>.

   [RFC5234]  Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", STD 68, RFC 5234,
              DOI 10.17487/RFC5234, January 2008,
              <https://www.rfc-editor.org/info/rfc5234>.

   [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>.

5.2.  Informative References

   [RFC4086]  Eastlake 3rd, D., Schiller, J., and S. Crocker,
              "Randomness Requirements for Security", BCP 106, RFC 4086,
              DOI 10.17487/RFC4086, June 2005,
              <https://www.rfc-editor.org/info/rfc4086>.

   [RFC6750]  Jones, M. and D. Hardt, "The OAuth 2.0 Authorization
              Framework: Bearer Token Usage", RFC 6750,
              DOI 10.17487/RFC6750, October 2012,
              <https://www.rfc-editor.org/info/rfc6750>.

Acknowledgements

   The definition of bearer tokens is from [RFC6750].

Author's Address

   Mark Nottingham
   Prahran VIC
   Australia

   Email: mnot@mnot.net
   URI:   https://www.mnot.net/