Internet DRAFT - draft-ietf-httpapi-api-catalog
draft-ietf-httpapi-api-catalog
Network Working Group K. Smith
Internet-Draft Vodafone
Intended status: Standards Track 4 March 2024
Expires: 5 September 2024
api-catalog: a well-known URI and link relation to help discovery of
APIs
draft-ietf-httpapi-api-catalog-02
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.
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
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This Internet-Draft will expire on 5 September 2024.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
1.2. Goals and non-goals . . . . . . . . . . . . . . . . . . . 3
1.3. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. Using the 'api-catalog' well-known URI . . . . . . . . . . . 4
3. Link relations . . . . . . . . . . . . . . . . . . . . . . . 4
4. Accounting for APIs distributed across multiple domains . . . 5
5. Internal use of api-catalog for private APIs . . . . . . . . 6
6. The API Catalog . . . . . . . . . . . . . . . . . . . . . . . 6
7. Conformance to RFC8615 . . . . . . . . . . . . . . . . . . . 7
7.1. Path prefix . . . . . . . . . . . . . . . . . . . . . . . 7
7.2. Supported URI schemes . . . . . . . . . . . . . . . . . . 7
7.3. Registration of the api-catalog well-known URI . . . . . 7
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
8.1. The api-catalog well-known URI . . . . . . . . . . . . . 7
8.2. The api-catalog link relation . . . . . . . . . . . . . . 8
8.3. the api-catalog Profile URI . . . . . . . . . . . . . . . 8
9. Security Considerations . . . . . . . . . . . . . . . . . . . 8
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
10.1. Normative References . . . . . . . . . . . . . . . . . . 9
10.2. Informative References . . . . . . . . . . . . . . . . . 9
Appendix A. Example API Catalog document . . . . . . . . . . . . 10
A.1. Using Linkset with RFC8615 relations . . . . . . . . . . 10
A.2. Using Linkset with bookmarks . . . . . . . . . . . . . . 12
Appendix B. Acknowledgements . . . . . . . . . . . . . . . . . . 13
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 13
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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 APIs. To facilitate automated discovery of this
information, and automated usage of the APIs, this document proposes:
* a well-known URI, 'api-catalog', as a reference to the URI of an
API Catalog document describing a Publisher's API endpoints.
* a link relation, 'api-catalog', of which the target resource is
the Publisher's API Catalog document.
1.1. Terminology
* 'Publisher' - an organisation, company or individual that
publishes one or more APIs for usage by external third parties.
1.2. 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.
1.3. Requirements Language
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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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:
* SHOULD publish the /.well-known/api-catalog URI at a predictable
location. For example as companies typically own a .com TLD, a
predictable location for the company 'example' would be
https://www.example.com/.well-known/api-catalog
* SHALL resolve an HTTP(S) GET request to /.well-known/api-catalog
and return an API catalog document ( as described in Section 6 ).
* SHOULD resolve an HTTP(S) HEAD request to /.well-known/api-catalog
with a response including a Link header with the relation(s)
defined in Section 3
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.
3. Link relations
* "api-catalog": the 'api-catalog' link relation identifies a target
resource that represents a list of APIs available from the
Publisher of the context resource. The target resource URI may be
./well-known/api-catalog , or any other URI chosen by the
Publisher. For example, the Publisher 'example.com' could include
the api-catalog link relation in the HTTP header and/or content
payload when responding to a request to https://example.com :
HTTP/1.1 200 OK
Content-Type: text/html; charset=UTF-8
Location: http\://www.example.com/
Link: </my_api_catalog.json.>; rel=api-catalog
Content-Length: 356
<!DOCTYPE HTML>
<html>
<head>
<title>Welcome to Example Publisher</title>
</head>
<body>
<p/><a href="my_api_catalog.json" rel="api-catalog">Example Publisher's APIs</a>.</p>
<p>(remainder of content)</p>
</body>
</html>
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* "item" [RFC9264]. When used in an API Catalog document, the
'item' link relation identifies a target resource that represents
an API that is a member of the API Catalog.
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:
* the Publisher publish the api-catalog well-known URI at a
predictable location, e.g. example.com/.well-known/api-catalog .
* the Publisher also publish the api-catalog well-known URI at each
of their API domains e.g. apis.example.com/.well-known/api-
catalog, developer.example.net/.well-known/api-catalog etc.
* an HTTP GET request to any of these URIs should return the same
result, namely, the API Catalog document.
* Since the physical location (URL) of the API Catalog document is
decided by the Publisher, and may change, it is RECOMMENDED that
the Publisher choose one of their instances of .well-known/api-
catalog as a canonical reference to the location of the latest API
Catalog. The Publisher's other instances of ./well-known/api-
catalog SHOULD redirect to this canonical instance of /.well-
known/api-catalog , using HTTP Status Code 308 Permanent Redirect
[RFC9110], to ensure the latest API Catalog is returned.
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:
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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.
There is no mandated format for the API Catalog document: the
Publisher is free to choose any format that supports the automated
discovery, and machine (and human) usage of their APIs. However, it
is RECOMMENDED to use a linkset [RFC9264] of API endpoints (see
Appendix A for an example).
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:
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* (RECOMMENDED) A linkset [RFC9264] of API endpoints and information
to facilitate API usage. The linkset SHOULD include a profile
parameter (section 5 of [RFC9264]) with the Profile URI
'https://datatracker.ietf.org/doc/draft-ietf-httpapi-api-catalog'
to indicate the linkset is representing an API Catalog document as
defined above.
* An APIs.json document [APIsjson]
* API bookmarks that represent an API entry-point URI, which may be
followed to discover purpose and usage
* A RESTDesc semantic description for hypermedia APIs [RESTdesc]
* A Hypertext Application Language document [HAL]
* An extension to the Schema.org WebAPI type [WebAPIext]
Appendix A includes example API Catalog documents based on the
linkset format.
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 prefix
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. Registration of the api-catalog well-known URI
See Section 8 considerations below.
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 [RFC6415].
URI suffix: api-catalog
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Specification document(s): draft-ietf-httpapi-api-catalog-02
Related information: The "api-catalog" documents obtained from the
same host using the HTTP and HTTPS protocols (using default ports)
MUST be identical.
8.2. The api-catalog link relation
This specification registers the "api-catalog" link relation by
following the procedures per section 4.2.2 of [RFC8288]
* Relation Name: api-catalog
* Description: Identifies a catalog of APIs published by the context
Publisher.
* Reference: draft-ietf-httpapi-api-catalog-02
8.3. the api-catalog Profile URI
This specification registers "https://datatracker.ietf.org/doc/draft-
ietf-httpapi-api-catalog" in the "Profile URIs" registry according to
[RFC7284].
o Profile URI: https://datatracker.ietf.org/doc/draft-ietf-httpapi-
api-catalog
o Common Name: API Catalog
o Description: A profile URI to request or signal a linkset
representing an API Catalog.
o Reference: draft-ietf-httpapi-api-catalog-02
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 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
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10.1. 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>.
[RFC6415] Hammer-Lahav, E., Ed. and B. Cook, "Web Host Metadata",
RFC 6415, DOI 10.17487/RFC6415, October 2011,
<https://www.rfc-editor.org/info/rfc6415>.
[RFC7284] Lanthaler, M., "The Profile URI Registry", RFC 7284,
DOI 10.17487/RFC7284, June 2014,
<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,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8288] Nottingham, M., "Web Linking", RFC 8288,
DOI 10.17487/RFC8288, October 2017,
<https://www.rfc-editor.org/info/rfc8288>.
[RFC8615] Nottingham, M., "Well-Known Uniform Resource Identifiers
(URIs)", RFC 8615, DOI 10.17487/RFC8615, May 2019,
<https://www.rfc-editor.org/info/rfc8615>.
[RFC9110] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
Ed., "HTTP Semantics", STD 97, RFC 9110,
DOI 10.17487/RFC9110, June 2022,
<https://www.rfc-editor.org/info/rfc9110>.
[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, July 2022,
<https://www.rfc-editor.org/info/rfc9264>.
10.2. Informative References
[APIsjson] Kin Lane and Steve Willmott, "APIs.json", 15 September
2020, <http://apisjson.org/format/apisjson_0.16.txt>.
[HAL] Mike Kelly, "JSON Hypertext Application Language", 15
September 2020, <https://datatracker.ietf.org/doc/html/
draft-kelly-json-hal-11>.
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[OAS] Darrel Miller, Jeremy Whitlock, Marsh Gardiner, Mike
Ralphson, Ron Ratovsky, and Uri Sarid, "OpenAPI
Specification 3.1.0", 15 February 2021,
<https://spec.openapis.org/oas/latest>.
[RESTdesc] Ruben Verborgh, Erik Mannens, Rick Van de Walle, and
Thomas Steiner, "RESTdesc", 15 September 2023,
<http://apisjson.org/format/apisjson_0.16.txt>.
[RFC8631] Wilde, E., "Link Relation Types for Web Services",
RFC 8631, DOI 10.17487/RFC8631, July 2019,
<https://www.rfc-editor.org/info/rfc8631>.
[WebAPIext]
Mike Ralphson and Nick Evans, "WebAPI type extension", 8
July 2020,
<https://webapi-discovery.github.io/rfcs/rfc0001.html>.
Appendix A. Example API Catalog document
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-know/api-catalog HTTP/1.1
Host: example.com
Accept: application/linkset+json
Server response:
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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="https://datatracker.ietf.org/doc/draft-ietf-httpapi-api-catalog"
{
"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"
}
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],
"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:
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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="https://datatracker.ietf.org/doc/draft-ietf-httpapi-api-catalog"
[
{ "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
Email: kevin.smith@vodafone.com
URI: https://www.vodafone.com
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