The "dereferenceable identifier" pattern
draft-bormann-t2trg-deref-id-00

Thing-to-Thing Research Group                                 C. Bormann
Internet-Draft                                    Universität Bremen TZI
Intended status: Informational                           5 November 2022
Expires: 9 May 2023

                The "dereferenceable identifier" pattern
                    draft-bormann-t2trg-deref-id-00

Abstract

   In a protocol or an application environment, it is often important to
   be able to create unambiguous identifiers for some meaning (concept
   or some entity).

   Due to the simplicity of creating URIs, these have become popular for
   this purpose.  Beyond the purpose of identifiers to be uniquely
   associated with a meaning, some of these URIs are in principle
   _dereferenceable_, so something can be placed that can be retrieved
   when encountering such a URI.

   The present -00 version is a stub to draw some attention to the
   opportunity that this pattern would benefit from a common
   description, documenting its benefits and pitfalls, and some
   mitigations for the latter.

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-bormann-t2trg-deref-id/.

   Discussion of this document takes place on the t2trg Research Group
   mailing list (mailto:t2trg@irtf.org), which is archived at
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   Source for this draft and an issue tracker can be found at
   https://github.com/cabo/deref-id.

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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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Examples for "dereferenceable identifiers"  . . . . . . . . .   3
     2.1.  Protocol and Protocol Version identifiers . . . . . . . .   3
     2.2.  Concept identifiers . . . . . . . . . . . . . . . . . . .   3
     2.3.  MORE EXAMPLES . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Pitfalls  . . . . . . . . . . . . . . . . . . . . . . . . . .   4
     3.1.  Server overload . . . . . . . . . . . . . . . . . . . . .   4
     3.2.  Longevity of identifiers  . . . . . . . . . . . . . . . .   4
     3.3.  Redirect ambiguities  . . . . . . . . . . . . . . . . . .   5
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   5.  Security considerations . . . . . . . . . . . . . . . . . . .   5
   6.  Informative References  . . . . . . . . . . . . . . . . . . .   5
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .   6
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   (Please see abstract.)

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2.  Examples for "dereferenceable identifiers"

   This section is intended to present a number of examples where
   dereferenceable identifiers are in use in a protocol, including
   existing discussion about constraints on their usage, the benefits
   claimed for this constrained usage, and remaining issues.

2.1.  Protocol and Protocol Version identifiers

   Many protocols based on XML or JSON include a protocol or protocol
   version identifier in the heading to a data item.

   E.g., [JSO] defines a language for data models that contain an
   identifier to the language version in use, here https://json-
   schema.org/draft/2020-12/schema.  The model that can be retrieved
   from this URI in turn contains further dereferenceable identifiers
   that point to further details.

   Section 8.1.1 of [JSO] has this:

   |  If this URI identifies a retrievable resource, that resource
   |  SHOULD be of media type "application/schema+json".

   So it acknowledges that the dereferenceability is optional, but does
   place further restrictions on what can be the result of a successful
   dereference: another one of these data models, which in turn contain
   further dereferenceable identifiers.

2.2.  Concept identifiers

   The _problem details_ format [PROBLEM] uses a dereferenceable
   identifier for its "type" field.  The value is a URI that "identifies
   the specific "problem type" (e.g., "out of credit")" (Section 1 of
   [PROBLEM]).

   Section 3.1.1 of [PROBLEM] has this:

   |  If the type URI is a locator (e.g., those with a "http" or "https"
   |  scheme), dereferencing it SHOULD provide human-readable
   |  documentation for the problem type (e.g., using HTML [HTML5]).

   but then warns:

   |  However, consumers SHOULD NOT automatically dereference the type
   |  URI, unless they do so when providing information to developers
   |  (e.g., when a debugging tool is in use).

   Section 5 of [PROBLEM] further details:

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   |  A problem's type URI SHOULD resolve to HTML [HTML5] documentation
   |  that explains how to resolve the problem.

   This becomes even more interesting as Section 5.2 of [PROBLEM] then
   gives this advice:

   |  Registrations MAY use the prefix "https://iana.org/assignments/
   |  http- problem-types#" for the type URI.

   A reference to the place where registrations for these items are
   managed is certainly desirable, however, the implications on the
   management of fragment identifiers in the HTML documents that IANA
   generates from registration information are an example for the
   increased complexity dereferenceable identifiers may place on the
   owners of the URI space employed.

2.3.  MORE EXAMPLES

   There are a lot more examples in published RFCs; add them to this
   document.

3.  Pitfalls

3.1.  Server overload

   If a data item containing dereferenceable identifier(s) becomes
   widely distributed, naive implementations that handle such a data
   item might dereference these identifiers as part of a routine
   operation.  Many definitions of dereferenceable identifiers contain
   admonitions that such a behavior can cause an implosion of requests
   on the server(s) for the URI.

3.2.  Longevity of identifiers

   Dereferenceable URIs usually contain domain names, whose ownership
   can change.  As a result, and for other reasons as well, parts of the
   name space of an origin may come under new administration, which can
   change the policies that apply to resources made available there.

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   These are problems of such URIs in general (and can be mitigated by
   going to a non-dereferenceable kind of URIs such as one based on the
   'tag' uri scheme [TAG]).  However, the problems are exacerbated by
   their use as a dereferenceable identifier.  The new owner/
   administrator might more easily accept that a certain chunk of their
   URI space should not be used (which suffices for a non-
   dereferenceable identifier based on this kind of URI namespace) than
   that certain content needs to be offered there (potentially
   presenting non-trivial loads, some mechanisms needed to update that
   information, and legal liabilities that are hard to assess).

3.3.  Redirect ambiguities

   Dereferencing an identifier may involve following some redirections;
   whether that following is actually implied, or desired (or even
   desirable) is rarely being discussed.

4.  IANA Considerations

   This document makes no concrete requests on IANA, but does point out
   that IANA resources might be a good target for a certain class of
   dereferenceable identifiers.

5.  Security considerations

   The ability to create a denial of service attack by pointing a
   dereferenceable identifier into a popular data item that is widely
   distributed is implied by the discussion in Section 2, alongside with
   some recommendations for implementers that would mitigate such
   attacks.  A problem with such recommendations is that they need to be
   followed by implementations that are using dereferenceable
   identifiers, which might not care much.

6.  Informative References

   [JSO]      Wright, A., Andrews, H., Hutton, B., and G. Dennis, "JSON
              Schema: A Media Type for Describing JSON Documents", Work
              in Progress, Internet-Draft, draft-bhutton-json-schema-01,
              10 June 2022, <https://www.ietf.org/archive/id/draft-
              bhutton-json-schema-01.txt>.

   [PROBLEM]  Nottingham, M., Wilde, E., and S. Dalal, "Problem Details
              for HTTP APIs", Work in Progress, Internet-Draft, draft-
              ietf-httpapi-rfc7807bis-04, 5 September 2022,
              <https://www.ietf.org/archive/id/draft-ietf-httpapi-
              rfc7807bis-04.txt>.

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   [TAG]      Kindberg, T. and S. Hawke, "The 'tag' URI Scheme",
              RFC 4151, DOI 10.17487/RFC4151, October 2005,
              <https://www.rfc-editor.org/info/rfc4151>.

Acknowledgements

   Christian Amsüss pointed out that this document would be good to
   have.

Author's Address

   Carsten Bormann
   Universität Bremen TZI
   Postfach 330440
   D-28359 Bremen
   Germany
   Phone: +49-421-218-63921
   Email: cabo@tzi.org

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