Internet DRAFT - draft-young-md-query
draft-young-md-query
Network Working Group I.A. Young, Ed.
Internet-Draft Independent
Intended status: Informational 7 January 2024
Expires: 10 July 2024
Metadata Query Protocol
draft-young-md-query-20
Abstract
This document defines a simple protocol for retrieving metadata about
named entities, or named collections of entities. The goal of the
protocol is to profile various aspects of HTTP to allow requesters to
rely on certain, rigorously defined, behaviour.
This document is a product of the Research and Education Federations
(REFEDS) Working Group process.
Editorial Note (To be removed by RFC Editor before publication)
Discussion of this draft takes place on the MDX mailing list
(mdx@lists.iay.org.uk), which is accessed from [MDX.list].
XML versions, latest edits and the issues list for this document are
available from [md-query].
The changes in this draft are summarized in Appendix A.21.
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 10 July 2024.
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Copyright Notice
Copyright (c) 2024 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.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Notation and Conventions . . . . . . . . . . . . . . . . 4
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
2. Protocol Transport . . . . . . . . . . . . . . . . . . . . . 4
2.1. Transport Protocol . . . . . . . . . . . . . . . . . . . 4
2.2. HTTP Version . . . . . . . . . . . . . . . . . . . . . . 4
2.3. HTTP Method . . . . . . . . . . . . . . . . . . . . . . . 5
2.4. Request Headers . . . . . . . . . . . . . . . . . . . . . 5
2.5. Response Headers . . . . . . . . . . . . . . . . . . . . 5
2.6. Status Codes . . . . . . . . . . . . . . . . . . . . . . 6
2.7. Base URL . . . . . . . . . . . . . . . . . . . . . . . . 6
2.8. Content Negotiation . . . . . . . . . . . . . . . . . . . 7
3. Metadata Query Protocol . . . . . . . . . . . . . . . . . . . 7
3.1. Identifiers . . . . . . . . . . . . . . . . . . . . . . . 7
3.2. Protocol . . . . . . . . . . . . . . . . . . . . . . . . 7
3.2.1. Request by Identifier . . . . . . . . . . . . . . . . 7
3.2.2. Request All Entities . . . . . . . . . . . . . . . . 8
3.2.3. Response . . . . . . . . . . . . . . . . . . . . . . 8
3.2.4. Example Request and Response . . . . . . . . . . . . 9
4. Efficient Retrieval and Caching . . . . . . . . . . . . . . . 9
4.1. Conditional Retrieval . . . . . . . . . . . . . . . . . . 9
4.2. Content Caching . . . . . . . . . . . . . . . . . . . . . 9
4.3. Content Compression . . . . . . . . . . . . . . . . . . . 10
5. Protocol Extension Points . . . . . . . . . . . . . . . . . . 10
6. Security Considerations . . . . . . . . . . . . . . . . . . . 10
6.1. Integrity . . . . . . . . . . . . . . . . . . . . . . . . 10
6.2. Confidentiality . . . . . . . . . . . . . . . . . . . . . 10
6.3. Authentication . . . . . . . . . . . . . . . . . . . . . 10
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 11
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 11
9.1. Normative References . . . . . . . . . . . . . . . . . . 11
9.2. Informative References . . . . . . . . . . . . . . . . . 12
Appendix A. Change Log (to be removed by RFC Editor before
publication) . . . . . . . . . . . . . . . . . . . . . . 13
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A.1. Since draft-lajoie-md-query-01 . . . . . . . . . . . . . 13
A.2. Since draft-young-md-query-00 . . . . . . . . . . . . . . 13
A.3. Since draft-young-md-query-01 . . . . . . . . . . . . . . 14
A.4. Since draft-young-md-query-02 . . . . . . . . . . . . . . 14
A.5. Since draft-young-md-query-03 . . . . . . . . . . . . . . 14
A.6. Since draft-young-md-query-04 . . . . . . . . . . . . . . 14
A.7. Since draft-young-md-query-05 . . . . . . . . . . . . . . 15
A.8. Since draft-young-md-query-06 . . . . . . . . . . . . . . 15
A.9. Since draft-young-md-query-07 . . . . . . . . . . . . . . 15
A.10. Since draft-young-md-query-08 . . . . . . . . . . . . . . 15
A.11. Since draft-young-md-query-09 . . . . . . . . . . . . . . 15
A.12. Since draft-young-md-query-10 . . . . . . . . . . . . . . 15
A.13. Since draft-young-md-query-11 . . . . . . . . . . . . . . 15
A.14. Since draft-young-md-query-12 . . . . . . . . . . . . . . 16
A.15. Since draft-young-md-query-13 . . . . . . . . . . . . . . 16
A.16. Since draft-young-md-query-14 . . . . . . . . . . . . . . 16
A.17. Since draft-young-md-query-15 . . . . . . . . . . . . . . 16
A.18. Since draft-young-md-query-16 . . . . . . . . . . . . . . 16
A.19. Since draft-young-md-query-17 . . . . . . . . . . . . . . 16
A.20. Since draft-young-md-query-18 . . . . . . . . . . . . . . 16
A.21. Since draft-young-md-query-19 . . . . . . . . . . . . . . 16
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 16
1. Introduction
Many clients of web-based services are capable of consuming
descriptive metadata about a service in order to customize or obtain
information about the client's connection parameters. While the form
of the metadata (e.g., JSON, XML) and content varies between services
this document specifies a set of semantics for HTTP ([RFC7230] et
seq.) that allow clients to rely on certain behavior. The defined
behavior is meant to make it easy for clients to perform queries, to
be efficient for both requesters and responders, and to allow the
responder to scale in various ways.
The Research and Education Federations group ([REFEDS]) is the voice
that articulates the mutual needs of research and education identity
federations worldwide. It aims to represent the requirements of
research and education in the ever-growing space of access and
identity management.
From time to time REFEDS will wish to publish a document in the
Internet RFC series. Such documents will be published as part of the
RFC Independent Submission Stream [RFC4844]; however the REFEDS
working group sign-off process will have been followed for these
documents, as described in the REFEDS Participant's Agreement
[REFEDS.agreement].
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This document is a product of the REFEDS Working Group process.
1.1. Notation and 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 makes use of the Augmented BNF metalanguage defined in
[STD68].
1.2. Terminology
entity: A single logical construct for which metadata may be
asserted. Generally this is a network accessible service.
metadata: A machine readable description of certain entity
characteristics. Generally metadata provides information such as
end point references, service contact information, etc.
2. Protocol Transport
The metadata query protocol seeks to fully employ the features of the
HTTP protocol. Additionally this specification makes mandatory some
optional HTTP features.
2.1. Transport Protocol
The metadata query protocol makes use of the HTTP protocol
([RFC7230]) to transmit requests and responses. The underlying HTTP
connection MAY make use of any appropriate transport protocol. In
particular, the HTTP connection MAY make use of either TCP or TLS at
the transport layer. See the Security Considerations section for
guidance in choosing an appropriate transport protocol.
2.2. HTTP Version
Requests from clients MUST NOT use an HTTP version prior to version
1.1. Responders MUST reply to such requests using status code 505,
"HTTP Version Not Supported".
Protocol responders MUST support requests using HTTP version 1.1, and
MAY support later versions.
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2.3. HTTP Method
All metadata query requests MUST use the GET method.
2.4. Request Headers
All metadata query requests MUST include the following HTTP headers:
Accept - this header MUST contain the content-type identifying the
type, or form, of metadata to be retrieved. See section 5.3.2 of
[RFC7231].
All metadata query requests SHOULD include the following HTTP
headers:
Accept-Charset, see section 5.3.3 of [RFC7231]
Accept-Encoding, see section 5.3.4 of [RFC7231]
A metadata request to the same URL, after an initial request, MUST
include the following header:
If-None-Match, see section 3.2 of [RFC7232].
2.5. Response Headers
All successful metadata query responses (even those that return no
results) MUST include the following headers:
Content-Encoding - required if, and only if, content is
compressed. See section 3.1.2.2 of [RFC7231].
Content-Type, see section 3.1.1.5 of [RFC7231].
ETag, see section 2.3 of [RFC7232].
All metadata retrieval responses SHOULD include the following
headers:
Cache-Control, see section 5.2 of [RFC7234].
Content-Length, see section 3.3.2 of [RFC7230]
Last-Modified, see section 2.2 of [RFC7232].
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2.6. Status Codes
This protocol uses the following HTTP status codes:
200 "OK" - standard response code when returning requested
metadata
304 "Not Modified" - response code indicating requested metadata
has not been updated since the last request
400 "Bad Request" - response code indicating that the requester's
request was malformed in some fashion
401 "Unauthorized" - response code indicating the request must be
authenticated before requesting metadata
404 "Not Found" - indicates that the requested metadata could not
be found; this MUST NOT be used in order to indicate a general
service error.
405 "Method Not Allowed" - response code indicating that a non-GET
method was used
406 "Not Acceptable" - response code indicating that metadata is
not available in the request content-type
505 "HTTP Version Not Supported" - response code indicating that
HTTP/1.1 was not used
2.7. Base URL
Requests defined in this document are performed by issuing an HTTP
GET request to a particular URL ([STD66]). The final component of
the path to which requests are issued is defined by the requests
specified within this document. A base URL precedes such paths.
Such a base URL:
* MUST contain the scheme and authority components.
* MUST contain a path component ending with a slash ('/') character.
* MUST NOT include a query component.
* MUST NOT include a fragment identifier component.
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2.8. Content Negotiation
As there may be many representations for a given piece of metadata,
agent-driven content negotiation is used to ensure the proper
representation is delivered to the requester. In addition to the
required usage of the Accept header a responder SHOULD also support
the use of the Accept-Charset header.
3. Metadata Query Protocol
The metadata query protocol retrieves metadata either for all
entities known to the responder or for a named collection based on a
single "tag" or "keyword" identifier. A request returns information
for none, one, or a collection of entities.
3.1. Identifiers
The query protocol uses identifiers to "tag" metadata for single- and
multi-entity metadata collections. The assignment of such
identifiers to a particular metadata document is the responsibility
of the query responder. If a metadata collection already contains a
well known identifier it is RECOMMENDED that such a natural
identifier is used when possible. Any given metadata collection MAY
have more than one identifier associated with it.
An identifier used in the query protocol is a non-empty sequence of
arbitrary 8-bit characters:
id = 1*idchar
idchar = %x00-ff ; any encodable character
3.2. Protocol
3.2.1. Request by Identifier
A metadata query request for all entities tagged with a particular
identifier is performed by issuing an HTTP GET request to a URL
constructed as the concatenation of the following components:
* The responder's base URL.
* The string "entities/".
* A single identifier, percent-encoded appropriately for use as a
URL path segment (see sections 2.1 and 3.3 of [STD66]).
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For example, with a base URL of http://example.org/mdq/, a query for
the identifier foo would be performed by an HTTP GET request to the
following URL:
http://example.org/mdq/entities/foo
Correct encoding of the identifier as a URL path segment is critical
for interoperability. In particular:
The character '/' MUST be percent-encoded.
The space character MUST be encoded as '%20' and MUST NOT be
encoded as '+' as would be required in a query parameter.
For example, with a base URL of http://example.org/mdq/, a query for
the identifier "blue/green+light blue" would be performed by an HTTP
GET request to the following URL:
http://example.org/mdq/entities/blue%2Fgreen+light%20blue
3.2.2. Request All Entities
A metadata query request for all entities known to the responder is
performed by issuing an HTTP GET request to a URL constructed as the
concatenation of the following components:
* The responder's base URL.
* The string "entities".
For example, with a base URL of http://example.org/mdq/, a query for
all entities would be performed by an HTTP GET request to the
following URL:
http://example.org/mdq/entities
3.2.3. Response
The response to a metadata query request MUST be a document that
provides metadata for the given request in the format described by
the request's Accept header.
The responder is responsible for ensuring that the metadata returned
is valid. If the responder can not create a valid document it MUST
respond with a 406 status code. An example of such an error would be
the case where the result of the query is metadata for multiple
entities but the request content type does not support returning
multiple results in a single document.
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3.2.4. Example Request and Response
The following example demonstrates a metadata query request using a
base URL of http://metadata.example.org/service/ and the identifier
http://example.org/idp.
GET /service/entities/http:%2F%2Fexample.org%2Fidp HTTP/1.1
Host: metadata.example.org
Accept: application/samlmetadata+xml
Figure 1: Example Metadata Query Request
HTTP/1.x 200 OK
Content-Type: application/samlmetadata+xml
ETag: "abcdefg"
Last-Modified: Thu, 15 Apr 2010 12:45:26 GMT
Content-Length: 1234
<?xml version="1.0" encoding="UTF-8"?>
<EntityDescriptor entityID="http://example.org/idp"
xmlns="urn:oasis:names:tc:SAML:2.0:metadata">
....
Figure 2: Example Metadata Query Response
4. Efficient Retrieval and Caching
4.1. Conditional Retrieval
Upon a successful response the responder MUST return an ETag header
and MAY return a Last-Modified header as well. Requesters SHOULD use
either or both, with the ETag being preferred, in any subsequent
requests for the same resource.
In the event that a resource has not changed since the previous
request, the responder SHOULD send a 304 (Not Modified) status code
as a response.
4.2. Content Caching
Responders SHOULD include cache control information with successful
(200 status code) responses, assuming the responder knows when
retrieved metadata is meant to expire. The responder SHOULD also
include cache control information with 404 Not Found responses. This
allows the requester to create and maintain a negative-response
cache. When cache controls are used only the 'max-age' directive
SHOULD be used.
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4.3. Content Compression
As should be apparent from the required request and response headers
this protocol encourages the use of content compression. This is in
recognition that some metadata documents can be quite large or
fetched with relatively high frequency.
Requesters SHOULD support, and advertise support for, gzip
compression unless such usage would put exceptional demands on
constrained environments. Responders MUST support gzip compression.
Requesters and responders MAY support other compression algorithms.
5. Protocol Extension Points
The Metadata Query Protocol is extensible using the following
protocol extension points:
* Profiles of this specification may assign semantics to specific
identifiers, or to identifiers structured in particular ways.
* Profiles of this specification may define additional paths (other
than entities and entities/) below the base URL.
6. Security Considerations
6.1. Integrity
As metadata often contains information necessary for the secure
operation of interacting services it is RECOMMENDED that some form of
content integrity checking be performed. This may include the use of
TLS at the transport layer, digital signatures present within the
metadata document, or any other such mechanism.
6.2. Confidentiality
In many cases service metadata is public information and therefore
confidentiality is not required. In the cases where such
functionality is required, it is RECOMMENDED that both the requester
and responder support TLS. Other mechanisms, such as XML encryption,
MAY also be supported.
6.3. Authentication
All responders which require client authentication to view retrieved
information MUST support the use of HTTP basic authentication
([RFC7235], [RFC7617]) over TLS. Responders SHOULD also support the
use of X.509 client certificate authentication.
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7. IANA Considerations
This document has no actions for IANA.
8. Acknowledgements
The editor would like to acknowledge the following individuals for
their contributions to this document:
Scott Cantor (The Ohio State University)
Leif Johansson (SUNET)
Thomas Lenggenhager (SWITCH)
Joe St Sauver (University of Oregon)
Tom Scavo (Internet2)
Special acknowledgement is due to Chad LaJoie (Covisint) for his work
in editing previous versions of this specification.
9. References
9.1. 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>.
[RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Message Syntax and Routing",
RFC 7230, DOI 10.17487/RFC7230, June 2014,
<https://www.rfc-editor.org/info/rfc7230>.
[RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Semantics and Content", RFC 7231,
DOI 10.17487/RFC7231, June 2014,
<https://www.rfc-editor.org/info/rfc7231>.
[RFC7232] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Conditional Requests", RFC 7232,
DOI 10.17487/RFC7232, June 2014,
<https://www.rfc-editor.org/info/rfc7232>.
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[RFC7234] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
Ed., "Hypertext Transfer Protocol (HTTP/1.1): Caching",
RFC 7234, DOI 10.17487/RFC7234, June 2014,
<https://www.rfc-editor.org/info/rfc7234>.
[RFC7235] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Authentication", RFC 7235,
DOI 10.17487/RFC7235, June 2014,
<https://www.rfc-editor.org/info/rfc7235>.
[RFC7617] Reschke, J., "The 'Basic' HTTP Authentication Scheme",
RFC 7617, DOI 10.17487/RFC7617, September 2015,
<https://www.rfc-editor.org/info/rfc7617>.
[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>.
[STD66] 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>.
[STD68] 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>.
9.2. Informative References
[md-query] Young, I.A., Ed., "md-query Project",
<https://github.com/iay/md-query>.
[MDX.list] Young, I.A., Ed., "MDX Mailing List",
<http://lists.iay.org.uk/listinfo.cgi/mdx-iay.org.uk>.
[REFEDS] Research and Education Federations, "REFEDS Home Page",
<http://www.refeds.org/>.
[REFEDS.agreement]
Research and Education Federations, "REFEDS Participant's
Agreement",
<https://refeds.org/about/about_agreement.html>.
[RFC4844] Daigle, L., Ed. and IAB, "The RFC Series and RFC Editor",
RFC 4844, DOI 10.17487/RFC4844, July 2007,
<https://www.rfc-editor.org/info/rfc4844>.
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Appendix A. Change Log (to be removed by RFC Editor before publication)
A.1. Since draft-lajoie-md-query-01
Adopted as base for draft-young-md-query-00.
Updated author and list of contributors.
Changed ipr from "pre5378Trust200902" to "trust200902", submission
type from IETF to independent and category from experimental to
informational.
Added empty IANA considerations section.
Minor typographical nits but (intentionally) no substantive content
changes.
A.2. Since draft-young-md-query-00
Split into two documents: this one is as agnostic as possible around
questions such as metadata format and higher level protocol use
cases, a new layered document describes the detailed requirements for
SAML support.
Rewrite Section 3.2.1 to clarify construction of the request URL and
its relationship to the base URL.
Added Section 2.1 to clarify that the transport protocol underlying
HTTP may be either TCP or SSL/TLS.
Clarify position on HTTP versions (Section 2.2) which may be used to
underly this protocol.
Added Change Log modelled on draft-ietf-httpbis-http2.
Added a reference to [STD68]. Use ABNF to describe request syntax.
Replace transformed identifier concept with extended identifiers
(this also resulted in the removal of any discussion of specific
transformed identifier formats). Add grammar to distinguish basic
from extended identifiers.
Changed the required response when the result can not be validly
expressed in the requested format from 500 to 406.
Removed the '+' operator and all references to multiple identifiers
in queries. If more complex queries are required, these will be
reintroduced at a different path under the base URL.
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Added a section describing Protocol Extension Points.
A.3. Since draft-young-md-query-01
Added REFEDS RFC stream boilerplate.
Tidied up some normative language.
A.4. Since draft-young-md-query-02
Introduced a normative reference to [STD66].
Reworked the definition of the base URL so that a non-empty path
ending with '/' is required. This allows the definition of request
URLs to be simplified.
Clarified the definition of the base URL to exclude a query
component; corrected the terminology for the fragment identifier
component.
Added the definition for the query for all entities in Section 3.2.2.
Corrected an example in Section 3.2.4 to include the required double
quotes in the value of an ETag header. Added text to clarify the
base URL and identifier being used in the example.
Simplified the definition of identifiers, so that any non-empty
identifier is accepted and no semantics are defined for particular
structures. Extended syntaxes such as the {sha1} notation for
transformed identifiers are now left to profiles.
Remove incidental references to SSL.
Remove status code 501 ("not implemented") as it is no longer
referenced.
A.5. Since draft-young-md-query-03
Correct a typo in the identifier grammar.
A.6. Since draft-young-md-query-04
Updated to rely on the new definition of HTTP/1.1 in [RFC7230] et
seq. instead of RFC 2616.
Corrected Section 3.2.3 to indicate that the request contains an
Accept header, not a Content-Type header.
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Added an Editorial Note to help direct readers back to the
discussion.
A.7. Since draft-young-md-query-05
Remove unnecessary percent-encoding of a ':' character in the example
in Section 3.2.4.
Removed use of the ambiguous term "URL-encoded" in Section 3.2.1.
Instead, indicate that the encoding must correspond to the rules for
encoding a URL path segment specifically, and call out some of the
more important implications arising from that. Added a new example
illustrating these implications.
Updated the description of conditional retrieval in Section 4.1 to
make the use of a 304 (Not Modified) status code a normative but non-
mandatory obligation on the responder, not simply a description of
what the requester will receive.
A.8. Since draft-young-md-query-06
No substantive changes.
A.9. Since draft-young-md-query-07
No substantive changes.
A.10. Since draft-young-md-query-08
Modernise normative language to include [RFC8174].
Reference [RFC7617] instead of the Internet-Draft.
Improved references to RFCs.
A.11. Since draft-young-md-query-09
No substantive changes.
A.12. Since draft-young-md-query-10
No substantive changes.
A.13. Since draft-young-md-query-11
No substantive changes.
Young Expires 10 July 2024 [Page 15]
Internet-Draft Metadata Query Protocol January 2024
A.14. Since draft-young-md-query-12
No substantive changes.
A.15. Since draft-young-md-query-13
No substantive changes.
A.16. Since draft-young-md-query-14
No substantive changes.
A.17. Since draft-young-md-query-15
No substantive changes.
A.18. Since draft-young-md-query-16
No substantive changes.
A.19. Since draft-young-md-query-17
No substantive changes.
A.20. Since draft-young-md-query-18
Formatting changes to allow rendering with xml2rfc version 3.
A.21. Since draft-young-md-query-19
No substantive changes.
Author's Address
Ian A. Young (editor)
Independent
Email: ian@iay.org.uk
Young Expires 10 July 2024 [Page 16]
