Internet-Draft api-catalog well-known URI October 2024
Smith Expires 21 April 2025 [Page]
Workgroup:
Network Working Group
Internet-Draft:
draft-ietf-httpapi-api-catalog-05
Published:
Intended Status:
Standards Track
Expires:
Author:
K. Smith
Vodafone

api-catalog: a well-known URI and link relation to help discovery of APIs

Abstract

This document defines the "api-catalog" well-known URI and link relation. It is intended to facilitate automated discovery and usage of the APIs published by a given organisation or individual. A request to the api-catalog resource will return a document providing information about, and links to, the publisher's APIs.

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://ietf-wg-httpapi.github.io/api-catalog/draft-ietf-httpapi-api-catalog.html. Status information for this document may be found at https://datatracker.ietf.org/doc/draft-ietf-httpapi-api-catalog/.

Discussion of this document takes place on the Building Blocks for HTTP APIs Working Group mailing list (mailto:httpapi@ietf.org), which is archived at https://mailarchive.ietf.org/arch/browse/httpapi/. Subscribe at https://www.ietf.org/mailman/listinfo/httpapi/.

Source for this draft and an issue tracker can be found at https://github.com/ietf-wg-httpapi/api-catalog.

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/.

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This Internet-Draft will expire on 21 April 2025.

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Table of Contents

1. Introduction

An organisation or individual may publish Application Programming Interfaces (APIs) to encourage requests for interaction from external parties. Such APIs must be discovered before they may be used - i.e., the external party needs to know what APIs a given publisher exposes, their purpose, any policies for usage, and the endpoint to interact with each API. To facilitate automated discovery of this information, and automated usage of the APIs, this document proposes:

1.1. Goals and non-goals

The primary goal is to facilitate the automated discovery of a Publisher's public API endpoints, along with metadata that describes the purpose and usage of each API, by specifying a well-known URI [RFC8615] that returns an API catalog document. The API catalog document is primarily machine-readable to enable automated discovery and usage of APIs, and it may also include links to human-readable documentation.

Non-goals: this document does not mandate paths for API endpoints. i.e., it does not mandate that my_example_api's endpoint should be example.com/.well-known/api-catalog/my_example_api , nor even to be hosted at example.com (although it is not forbidden to do so). This document does not mandate a specific format for the API catalog document, although it does suggest some existing formats and provide a recommendation.

1.2. 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. These words may also appear in this document in lower case as plain English words, absent their normative meanings.

The term "content negotiation" and "status code" are from [HTTP]. The term well-known URI is from [RFC8615].

The term "Publisher" refers to an organisation, company or individual that publishes one or more APIs for usage by external third parties.

2. Using the 'api-catalog' well-known URI

The api-catalog well-known URI is intended for HTTP(S) servers that publish APIs. As the key aim is to facilitate discovery and usage of APIs, a Publisher supporting this URI:

The location (URL) of the API Catalog document is decided by the Publisher: the ./well-known/api-catalog URI provides a convenient reference to that URL.

4. Accounting for APIs distributed across multiple domains

A Publisher ('example') may have their APIs hosted across multiple domains that they manage: e.g., at example.com, developer.example.com, apis.example.com, apis.example.net etc. They may also use a third party API hosting provider which hosts APIs on a distinct domain.

To account for this scenario, it is RECOMMENDED that:

As illustration, if the Publisher's primary API portal is apis.example.com, then apis.example.com/.well-known/api-catalog should resolve to the location of the latest API Catalog document. If the Publisher is also the domain authority for example.net, which also hosts a selection of their APIs, then a request to www.example.net/.well-known/api-catalog SHOULD return a redirect as follows.

Client request:

GET /.well-known/api-catalog HTTP/1.1
User-Agent: curl/7.16.3 libcurl/7.16.3 OpenSSL/0.9.7l zlib/1.2.3
Host: www.example.net

Server response:

HTTP/1.1 308 Permanent Redirect
Content-Type: text/html; charset=UTF-8
Location: http://apis.example.com/.well-known/api-catalog
Content-Length: 356

<!DOCTYPE HTML>
  <html>
    <head>
      <title>Permanent Redirect</title>
      <meta http-equiv="refresh" content="0; url=https://apis.example.com/.well-known/api-catalog">
    </head>
    <body>
      <p>Redirected to:  <a href=https://apis.example.com/.well-known/api-catalog>https://apis.example.com/.well-known/api-catalog</a>.</p>
    </body>
  </html>

5. Internal use of api-catalog for private APIs

A Publisher may wish to use the api-catalog well-known URI on their internal network, to signpost authorised users (e.g. company employees) towards internal/private APIs not intended for third-party use. This scenario may incur additional security considerations, as noted in Section 9.

6. The API Catalog

The API Catalog is a document listing hyperlinks to a Publisher's APIs. The Publisher may host this API Catalog document at any URI(s) they choose. Hence the API Catalog document URI of example.com/my_api_catalog.json can be requested directly, or via a request to example.com/.well-known/api-catalog, which the Publisher will resolve to example.com/my_api_catalog.

The Publisher MUST publish the API Catalog document in the Linkset format application/linkset+json (section 4.2 of [RFC9264]). In addition, the Publisher MAY make additional formats available via content negotiation (section 5.3 of [HTTP]) to their /.well-known/api-catalog location. A non-exhaustive list of such formats that support the automated discovery, and machine (and human) usage of a Publisher's APIs, is listed below.

The API Catalog document MUST include hyperlinks to API endpoints, and is RECOMMENDED to include useful metadata, such as usage policies, API version information, links to the OpenAPI Specification [OAS] definitions for each API, etc. . If the Publisher does not include these metadata directly in the API Catalog document, they SHOULD make that metadata available at the API endpoint URIs they have listed (see Appendix A.2 for an example).

Some suitable API Catalog document formats include:

If a Publisher already lists their APIs in a format other than linkset but wish to utiise the /.well-known/api-catalog URI, then: * they MUST also implement a linkset with, at minimum, hyperlinks to API endpoints - see the exmple of Using Linkset with bookmarks in Appendix A. * they MAY support content negotiation at the /.well-known/api-catalog URI to allow their existing format to be returned.

7. Conformance to RFC8615

The requirements in section 3 of [RFC8615] for defining Well-Known Uniform Resource Identifiers are met as follows:

7.1. Path suffix

The api-catalog URI SHALL be appended to the /.well-known/ path-prefix for "well-known locations".

7.2. Supported URI schemes

The api-catalog well-known URI may be used with the HTTP and HTTPS URI schemes.

7.3. Formats and associated media types

A /.well-known/api-catalog location MUST support the Linkset [RFC9264] format of application/linkset+json, and MAY also support the other formats via content negotiation.

8. IANA Considerations

8.1. The api-catalog well-known URI

This specification registers the "api-catalog" well-known URI in the Well-Known URI Registry as defined by [RFC8615].

  • URI suffix: api-catalog

  • Change Controller: IETF

  • Specification document(s): THIS-RFC

  • Status: permanent

  • Related information: The "api-catalog" documents obtained from the same host using the HTTP and HTTPS protocols (using default ports) MUST be identical.

8.3. the api-catalog Profile URI

This specification registers "THIS-RFC-URL" in the "Profile URIs" registry according to [RFC7284].

  • Profile URI: THIS-RFC-URL

  • Common Name: API Catalog

  • Description: A profile URI to request or signal a linkset representing an API Catalog.

  • Reference: THIS-RFC

RFC Editor's Note: IANA is kindly requested to replace all instances of THIS-RFC and THIS-RFC-URL with the actual RFC number/URL once assigned.

9. Security Considerations

For all scenarios: the Publisher SHOULD perform a security and privacy review of the API Catalog prior to deployment, to ensure it does not leak personal, business or other sensitive metadata, nor expose any vulnerability related to the APIs listed.

For the internal/private APIs scenario: the Publisher SHOULD take steps to ensure that appropriate access controls are in place to ensure only authorised users access the internal api-catalog well-known URI.

10. References

10.1. Normative References

[HTTP]
Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke, Ed., "HTTP Semantics", STD 97, RFC 9110, DOI 10.17487/RFC9110, , <https://www.rfc-editor.org/rfc/rfc9110>.
[RFC2119]
Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, , <https://www.rfc-editor.org/info/rfc2119>.
[RFC7284]
Lanthaler, M., "The Profile URI Registry", RFC 7284, DOI 10.17487/RFC7284, , <https://www.rfc-editor.org/info/rfc7284>.
[RFC8174]
Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, , <https://www.rfc-editor.org/info/rfc8174>.
[RFC8288]
Nottingham, M., "Web Linking", RFC 8288, DOI 10.17487/RFC8288, , <https://www.rfc-editor.org/info/rfc8288>.
[RFC8615]
Nottingham, M., "Well-Known Uniform Resource Identifiers (URIs)", RFC 8615, DOI 10.17487/RFC8615, , <https://www.rfc-editor.org/info/rfc8615>.
[RFC9264]
Wilde, E. and H. Van de Sompel, "Linkset: Media Types and a Link Relation Type for Link Sets", RFC 9264, DOI 10.17487/RFC9264, , <https://www.rfc-editor.org/info/rfc9264>.

10.2. Informative References

[APIsjson]
Kin Lane and Steve Willmott, "APIs.json", , <http://apisjson.org/format/apisjson_0.16.txt>.
[HAL]
Mike Kelly, "JSON Hypertext Application Language", , <https://datatracker.ietf.org/doc/html/draft-kelly-json-hal-11>.
[OAS]
Darrel Miller, Jeremy Whitlock, Marsh Gardiner, Mike Ralphson, Ron Ratovsky, and Uri Sarid, "OpenAPI Specification 3.1.0", , <https://spec.openapis.org/oas/latest>.
[RESTdesc]
Ruben Verborgh, Erik Mannens, Rick Van de Walle, and Thomas Steiner, "RESTdesc", , <http://apisjson.org/format/apisjson_0.16.txt>.
[RFC8631]
Wilde, E., "Link Relation Types for Web Services", RFC 8631, DOI 10.17487/RFC8631, , <https://www.rfc-editor.org/info/rfc8631>.
[WebAPIext]
Mike Ralphson and Nick Evans, "WebAPI type extension", , <https://webapi-discovery.github.io/rfcs/rfc0001.html>.

Appendix A. Example API Catalog documents

This section is informative, and provides and example of an API Catalog document using the RECOMMENDED linkset format.

A.1. Using Linkset with RFC8615 relations

This example uses the linkset format [RFC9264], and the following link relations defined in [RFC8631]:

  • "service-desc", used to link to a description of the API that is primarily intended for machine consumption.

  • "service-doc", used to link to API documentation that is primarily intended for human consumption.

  • "service-meta", used to link to additional metadata about the API, and is primarily intended for machine consumption.

  • "status", used to link to the API status (e.g. API "health" indication etc.) for machine and/or human consumption.

Client request:

GET .well-known/api-catalog HTTP/1.1
Host: example.com
Accept: application/linkset+json

Server response:

HTTP/1.1 200 OK
Date: Mon, 01 Jun 2023 00:00:01 GMT
Server: Apache-Coyote/1.1
Content-Type: application/linkset+json;
    profile="THIS-RFC-URL"

{
  "linkset": [
  {
    "anchor": "https://developer.example.com/apis/foo_api",
    "service-desc": [
      {
        "href": "https://developer.example.com/apis/foo_api/spec",
        "type": "application/yaml"
      }
    ],
    "status": [
      {
        "href": "https://developer.example.com/apis/foo_api/status",
        "type": "application/json"
      }
    ],
    "service-doc": [
      {
        "href": "https://developer.example.com/apis/foo_api/doc",
        "type": "text/html"
      }
    ],
    "service-meta": [
      {
        "href": "https://developer.example.com/apis/foo_api/policies",
        "type": "text/xml"
      }
    ]
  },
  {
    "anchor": "https://developer.example.com/apis/bar_api",
    "service-desc": [
      {
        "href": "https://developer.example.com/apis/bar_api/spec",
        "type": "application/yaml"
      }
    ],
    "status": [
      {
        "href": "https://developer.example.com/apis/bar_api/status",
       "type": "application/json"
      }
    ],
    "service-doc": [
      {
        "href": "https://developer.example.com/apis/bar_api/doc",
        "type": "text/plain"
      }
    ]
  },
  {
    "anchor": "https://apis.example.net/apis/cantona_api",
    "service-desc": [
      {
        "href": "https://apis.example.net/apis/cantona_api/spec",
        "type": "text/n3"
      }
    ],
    "service-doc": [
      {
        "href": "https://apis.example.net/apis/cantona_api/doc",
        "type": "text/html"
      }
    ]
  }
  ]
}

A.2. Using Linkset with bookmarks

This example also uses the linkset format [RFC9264], listing the API endpoints in an array of bookmarks. Each link shares the same context (the API Catalog) and "item" [RFC9264] link relation (to indicate they are an item in the catalog).The intent is that by following a bookmark link, a machine-client can discover the purpose and usage of each API, hence the document targeted by the bookmark link should support this.

Note in the example below, the context anchor is example/com/.well-known/api-catalog, however as explained above the context anchor may be any other URI at which the api-catalog is available.

Client request:

GET .well-know/api-catalog HTTP/1.1
Host: example.com
Accept: application/linkset+json

Server response:

HTTP/1.1 200 OK
Date: Mon, 01 Jun 2023 00:00:01 GMT
Server: Apache-Coyote/1.1
Content-Type: application/linkset+json;
    profile="THIS-RFC-URL"

[
  { "anchor": "https://example.com/.well-known/api-catalog",
    "item": [
      {"href": "https://developer.example.com/apis/foo_api"},
      {"href": "https://developer.example.com/apis/bar_api"},
      {"href": "https://developer.example.com/apis/cantona_api"}
    ]
  }
]

Appendix B. Acknowledgements

Thanks to Phil Archer, Ben Bucksch, Sanjay Dalal, Max Maton, Darrel Miller, Mark Nottingham, Roberto Polli, Rich Salz, Herbert Van De Sompel and Erik Wilde for their suggestions and feedback.

Author's Address

Kevin Smith
Vodafone
URI: https://www.vodafone.com