Solid Protocol

Editor’s Draft, 2021-05-12

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https://solidproject.org/TR/protocol
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Abstract

This document connects a set of specifications that, together, provide applications with secure and permissioned access to externally stored data in an interoperable way.

Status of This Document

This section describes the status of this document at the time of its publication.

This document was published by the Solid Community Group as an Editor’s Draft. The sections that have been incorporated have been reviewed following the Solid process. However, the information in this document is still subject to change. You are invited to contribute any feedback, comments, or questions you might have.

Publication as an Editor’s Draft does not imply endorsement by the W3C Membership. This is a draft document and may be updated, replaced or obsoleted by other documents at any time. It is inappropriate to cite this document as other than work in progress.

This document was produced by a group operating under the W3C Community Contributor License Agreement (CLA). A human-readable summary is available.

Introduction

The aims of the Solid project are in line with those of the Web itself: empowerment towards an equitable, informed and interconnected society. Solid adds to existing Web standards to realise a space where individuals can maintain their autonomy, control their data and privacy, and choose applications and services to fulfil their needs.

The Solid ecosystem encapsulates a set of specifications that are guided by the principles we have adopted and also the priority of our values. We acknowledge that every technical decision has ethical implications both for the end user (short-term) as well as society (long-term). To contribute towards a net positive social benefit, we use the Ethical Web Principles to orient ourselves. The consensus on the technical designs are informed by common use cases, implementation experience, and use.

An overarching design goal of the Solid ecosystem is to be evolvable and to provide fundamental affordances for decentralised Web applications for information exchange in a way that is secure and privacy respecting. In this environment, actors allocate identifiers for their content, shape and store data where they have access to, set access control policies, and use preferred applications and services to achieve them.

The general architectural principles of Solid specifications are borrowed from the Architecture of the World Wide Web. The components as described in each specification may evolve independently – according to the principle of orthogonality in order to increase the flexibility and robustness of the Solid ecosystem. With that, the specifications are loosely coupled and indicate which features overlap with those governed by another specification. Extensibility as well as variability also are taken into account in each specification.

The specifications in the ecosystem describe how Solid servers and clients can be interoperable by using Web communication protocols, global identifiers, authentication and authorization mechanisms, data formats and shapes, and query interfaces.

The specifications are accompanied with supplemental documents, such as Primers and Best Practices and Guidelines to help implementers to form a well-rounded understanding of the Solid ecosystem as well as ways to improve their implementations.

Definitions

A data pod is a place for storing documents, with mechanisms for controlling who can access what.

A Solid app is an application that reads or writes data from one or more data pods.

A read operation entails that information about a resource’s existence or its description can be known. [Source]

A write operation entails that information about resources can be created or removed. [Source]

An append operation entails that information can be added but not removed. [Source]

Namespaces

Prefixes and Namespaces
Prefix Namespace Description
rdf http://www.w3.org/1999/02/22-rdf-syntax-ns# [rdf-schema]
ldp http://www.w3.org/ns/ldp# [LDP]
solid http://www.w3.org/ns/solid/terms# Solid Terms
pim http://www.w3.org/ns/pim/space# Workspace Ontology
acl http://www.w3.org/ns/auth/acl# ACL Ontology

Conformance

All assertions, diagrams, examples, and notes are non-normative, as are all sections explicitly marked non-normative. Everything else is normative.

The key words “MUST”, “MUST NOT”, “REQUIRED”, “SHALL”, “SHALL NOT”, “SHOULD”, “SHOULD NOT”, “RECOMMENDED”, “MAY”, and “OPTIONAL” are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.

Hypertext Transfer Protocol

Solid clients and servers need to exchange data securely over the Internet, and they do so using the HTTP Web standard. This section describes in detail which parts of HTTP must be implemented by clients and servers.

Required Server-Side Implementation

A data pod MUST be an HTTP/1.1 server [RFC7230][RFC7231]. It SHOULD additionally be an HTTP/2 server [RFC7540] to improve performance, especially in cases where individual clients are expected to send high numbers of successive requests.

A data pod SHOULD use TLS connections through the https URI scheme in order to secure the communication between clients and servers. When both http and https are supported, all http URIs MUST redirect to their https counterparts using a response with a 301 status code and a Location header.

A data pod MUST implement the server part of HTTP/1.1 Conditional Requests [RFC7232] to ensure that updates requested by clients will only be applied if given preconditions are met. It SHOULD additionally implement the server part of HTTP/1.1 Caching [RFC7234] to improve performance. A data pod MAY implement the server part of HTTP/1.1 Range Requests [RFC7233] to further improve performance for large representations.

A data pod MUST implement the server part of HTTP/1.1 Authentication [RFC7235]. When a client does not provide valid credentials when requesting a resource that requires it (see WebID), the data pod MUST send a response with a 401 status code (unless 404 is preferred for security reasons).

A Solid server MUST reject PUT, POST and PATCH requests without the Content-Type header with a status code of 400. [Source]

Required Client-Side Implementation

A Solid client MUST be an HTTP/1.1 client [RFC7230][RFC7231]. It MAY additionally be an HTTP/2 client [RFC7540] to improve performance.

A Solid client MAY implement the client parts of HTTP/1.1 Conditional Requests [RFC7232] to only trigger updates when certain preconditions are met. It MAY implement HTTP/1.1 Caching [RFC7234] and HTTP/1.1 Range Requests [RFC7233] to improve performance.

A Solid client MUST implement the client part of HTTP/1.1 Authentication [RFC7235] if it needs to access resources requiring authentication (see WebID). When it receives a response with a 403 or 404 status code, it MAY repeat the request with different credentials.

A Solid client MUST use the Content-Type HTTP header in PUT, POST and PATCH requests [RFC7231]. [Source]

Uniform Resource Identifier

URI Slash Semantics

The slash (/) character in the URI path indicates hierarchical relationship segments, and enables relative referencing [RFC3986]. The semantics of the slash character is shared by servers and clients. Paths ending with a slash denote a container resource. [Source]

If two URIs differ only in the trailing slash, and the server has associated a resource with one of them, then the other URI MUST NOT correspond to another resource. Instead, the server MAY respond to requests for the latter URI with a 301 redirect to the former. [Source]. Behaviour pertaining to authorization MUST precede this optional redirect [Source]

URI Persistence

This section is non-normative.

Servers should not re-use URIs, regardless of the mechanism by which resources are created. Certain specific cases exist where URIs may be reinstated when it identifies the same resource, but only when consistent with Web architecture’s URI persistence [WEBARCH]. [Source]

Note: Servers that wish to disable URI re-use may want to use the 410 status code.

Resources

Storage

When a server supports a data pod, it MUST provide one or more storages (pim:Storage) – a space of URIs in which data can be accessed. A storage is the root container for all of its contained resources (see Resource Containment).

When a server supports multiple storages, the URIs MUST be allocated to non-overlapping space.

Servers exposing the storage resource MUST advertise by including the HTTP Link header with rel="type" targeting http://www.w3.org/ns/pim/space#Storage when responding to storage’s request URI.

Clients can determine a resource is of type storage by making an HTTP HEAD or GET request on the target URL, and checking for the Link header with rel="type" targeting http://www.w3.org/ns/pim/space#Storage.

Clients can determine the storage of a resource by moving up the URI path hierarchy until the response includes a Link header with rel="type" targeting http://www.w3.org/ns/pim/space#Storage. Clients may check the root path of a URI for the storage claim at any time.

Clients can discover a storage by making an HTTP GET request on the target URL to retrieve an RDF representation [RDF11-CONCEPTS], whose encoded RDF graph contains a relation of type http://www.w3.org/ns/pim/space#storage. The object of the relation is the storage (pim:Storage).

[Source] [Source]

When using Web Access Control (Web Access Control):

The root container (pim:Storage) MUST have an ACL auxiliary resource directly associated to it. The associated ACL document MUST include an authorization policy with acl:Control access privilege.

[Source]

Resource Containment

Solid has the notion of containers to represent a collection of linked resources to help with resource discovery and lifecycle management.

There is a 1-1 correspondence between containment triples and relative reference within the path name hierarchy. [Source]. It follows that all resources are discoverable from a container and that it is not possible to create orphan resources. [Source]

The representation and behaviour of containers in Solid corresponds to LDP Basic Container and MUST be supported. [Source]

Auxiliary Resources

Solid has the notion of auxiliary resources to provide supplementary information such as descriptive metadata, authorization policies, data shape constraints, digital rights or provenance record about a given resource (hereafter referred as the subject resource), and affects how resources and others associated with it are processed, served or interpreted.

Auxiliary resources are represented as RDF documents [RDF11-CONCEPTS].

Note: Where applicable, to promote self-describing resources, implementations and authors are encouraged to use the subject resource instead of the associated auxiliary resource.

Servers exposing auxiliary resources that are defined by this specification MUST have the same "origin" for both the resource and the associated auxiliary resource [RFC6454].

As per Deleting Resources, the lifecycle of auxiliary resources defined by this specification depend on the lifecycle of the subject resource.

This specification defines the following types of auxiliary resources:

Clients can discover auxiliary resources associated with a subject resource by making an HTTP HEAD or GET request on the target URL, and checking the HTTP Link header with the rel parameter [RFC8288].

Auxiliary Type Link Relation Definitions
Web Access Control acl [Solid Protocol]
Description Resource describedby [LDP]

The possibility of using URIs as relation types interchangeably or as alternate to the tokens above are under consideration:

  • http://www.w3.org/ns/auth/acl#accessControl
  • https://www.w3.org/ns/iana/link-relations/relation#describedby
  • https://www.w3.org/ns/iana/link-relations/relation#describes

Issue

Web Access Control

An auxiliary resource of type Web Access Control provides access control description of a subject resource (Web Access Control).

Servers MUST NOT directly associate more than one ACL auxiliary resource to a subject resource.

Description Resource

An auxiliary resource of type Description Resource provides a description of a subject resource ([LDP]).

Servers MUST NOT directly associate more than one description resource to a subject resource.

When an HTTP request targets a description resource, the server MUST apply the authorization policy that is used for the subject resource with which the description resource is associated.

Clients can discover resources that are described by description resources by making an HTTP HEAD or GET request on the target URL, and checking the HTTP Link header with a rel value of describes (inverse of the describedby relation) [RFC6892].

Reading and Writing Resources

Servers MUST respond with the 405 status code to requests using HTTP methods that are not supported by the target resource. [Source]

Resource Type Heuristics

When creating new resources, servers can determine an effective request URI’s type by examining the URI path ending (URI Slash Semantics).

When a successful PUT or PATCH request creates a resource, the server MUST use the effective request URI to assign the URI to that resource.

When a successful POST request creates a resource, the server MUST assign a URI to that resource. Servers MAY allow clients to suggest the URI of a resource created through POST, using the HTTP Slug header as defined in [RFC5023].

Note: Clients can use PUT and PATCH requests to assign a URI to a resource. Clients can use POST requests to have the server assign a URI to a resource.

[Source][Source].

Reading Resources

Servers MUST support the HTTP GET, HEAD and OPTIONS methods [RFC7231] for clients to read resources or to determine communication options. [Source]

When responding to authorized requests:

Servers MUST indicate their support for HTTP Methods by responding to HTTP GET and HEAD requests for the target resource with the HTTP Method tokens in the HTTP response header Allow.

Servers MUST indicate supported media types in the HTTP Accept-Patch [RFC5789], Accept-Post [LDP] and Accept-Put [The Accept-Put Response Header] response headers that correspond to acceptable HTTP methods listed in Allow header value in response to HTTP GET and HEAD requests.

Servers MAY include the HTTP Accept-Patch, Accept-Post and Accept-Put headers in the response of a OPTIONS * request.

[Source] [Source]

Writing Resources

When a server supports the HTTP PUT, POST and PATCH methods [RFC7231] this specification imposes the following requirements: [Source]

Servers MUST create intermediate containers and include corresponding containment triples in container representations derived from the URI path component of PUT and PATCH requests. [Source]

Servers MUST allow creating new resources with a POST request to URI path ending /. Servers MUST create a resource with URI path ending /{id} in container /. Servers MUST create a container with URI path ending /{id}/ in container / for requests including the HTTP Link header with rel="type" targeting a valid LDP container type. Servers MUST handle subsequent requests to the newly created container’s URI as if it is a valid LDP container type by including the HTTP response’s Link header. [Source]

When a POST method request targets a resource without an existing representation, the server MUST respond with the 404 status code. [Source]

When a PUT or PATCH method request targets an auxiliary resource, the server MUST create or update it. When a POST method request with the Slug header targets an auxiliary resource, the server MUST respond with the 403 status code and response body describing the error. [Source]

Servers MUST NOT allow HTTP POST, PUT and PATCH to update a container’s containment triples; if the server receives such a request, it MUST respond with a 409 status code. [Source]

Clients MAY use the HTTP If-None-Match header with a value of "*" to prevent an unsafe request method (eg. PUT, PATCH) from inadvertently modifying an existing representation of the target resource when the client believes that the resource does not have a current representation. [Source] [Source]

Servers MAY use the HTTP ETag header with a strong validator for RDF bearing representations in order to encourage clients to opt-in to using the If-Match header in their requests.

When using Web Access Control (Web Access Control):

To create or update an ACL resource (see Web Access Control), an acl:agent MUST have acl:Control privileges per the ACL inheritance algorithm on the resource directly associated with it. [Source]

Deleting Resources

When a server supports the HTTP DELETE method [RFC7231] this specification imposes the following requirements: [Source]

When a DELETE request targets storage’s root container or its associated ACL resource, the server MUST respond with the 405 status code. Server MUST exclude the DELETE method in the HTTP response header Allow in response to requests [RFC7231]. [Source]

When a contained resource is deleted, the server MUST also remove the corresponding containment triple, which has the effect of removing the deleted resource from the containing container. [Source]

When a contained resource is deleted, the server MUST also delete the associated auxiliary resources (see the Auxiliary Resources section).

When a DELETE request is made to a container, the server MUST delete the container if it contains no resources. If the container contains resources, the server MUST respond with the 409 status code and response body describing the error. [Source]

When using Web Access Control (Web Access Control):

To delete a resource, an acl:agent MUST have acl:Write privilege per the ACL inheritance algorithm on the resource and the containing container. [Source]

To delete an ACL resource (see Web Access Control), an acl:agent MUST have acl:Control privileges per the ACL inheritance algorithm on the resource directly associated with it. [Source]

This section is non-normative.

The server might perform additional actions, as described in the normative references like [RFC7231]. For example, the server could remove membership triples referring to the deleted resource, perform additional cleanup tasks for resources it knows are no longer referenced or have not been accessed for some period of time, and so on.

Subsequent GET requests to the deleted resource usually result in a 404 or 410 status code, although HTTP allows others. [Source] [Source]

As deleted resources can be reinstated with the same URI, access controls on the reinstated resource can change per the ACL inheritance algorithm. [Source]

Pertaining to events and loss of control mitigation: https://github.com/solid/specification/issues/41#issuecomment-534679278

Resource Representations

When a server creates a resource on HTTP PUT, POST or PATCH requests such that the request’s representation data encodes an RDF document [RDF11-CONCEPTS] (as determined by the Content-Type header), the server MUST accept GET requests on this resource when the value of the Accept header requests a representation in text/turtle or application/ld+json [Turtle] [JSON-LD11]. [Source] Source] [Source] [Source]

When a PUT, POST, PATCH or DELETE method request targets a representation URL that is different than the resource URL, the server MUST respond with a 307 or 308 status code and Location header specifying the preferred URI reference. [Source]

Notifications

A Solid server MUST conform to the LDN specification by implementing the Receiver parts to receive notifications and make Inbox contents available [LDN].

A Solid client MUST conform to the LDN specification by implementing the Sender or Consumer parts to discover the location of a resource’s Inbox, and to send notifications to an Inbox or to retrieve the contents of an Inbox [LDN].

WebSockets

For real-time communication between client and server about changes affecting a resource, Solid uses the WebSocket API [W3C-HTML] and the WebSocket Protocol.

WebSockets Pub-Sub

WebSockets Patching

Cross-Origin Resource Sharing

Solid apps typically access data from multiple sources. However, Web browsers by default prevent apps that run on one origin from accessing data on other origins. This cross-origin protection is a security mechanism that ensures malicious websites cannot simply read your profile or banking details from other websites. However, this reasonable default poses a problem even for benevolent Solid apps, which might have good reasons to access data from different places. For instance, a Solid app at https://app.example/ would be prevented from accessing data on https://guinan.example/ or https://darmok.example/, even when Guinan and Darmok have given the user of the app their permission to see some of their data.

For cases where the other origins have their own access protection mechanism — like within Solid — the browser’s built-in cross-origin protection is actually an obstacle rather than a feature. After all, data pods already ensure through access control that certain documents can only be accessed by specific people or applications. Preventively blocking apps from different origins thus introduces an unnecessary barrier.

Fortunately, Web servers can indicate to the browser that certain documents do not require cross-origin protection. This mechanism to selectively disable that protection is called Cross-Origin Resource Sharing or CORS [FETCH]. By responding to browser requests with a specific combination of HTTP headers, servers can indicate which actions are allowed for a given resource. For a Solid data pod, the goal is to allow all actions on the CORS level, such that the deeper access control layer can exert full control over the app’s allowed permissions. The next section describes how to achieve this through the right HTTP header configuration.

Required Server-Side Implementation

A data pod MUST implement the CORS protocol [FETCH] such that, to the extent possible, the browser allows Solid apps to send any request and combination of request headers to the data pod, and the Solid app can read any response and response headers received from the data pod. If the data pod wishes to block access to a resource, this MUST NOT happen via CORS but MUST instead be communicated to the Solid app in the browser through HTTP status codes such as 401, 403, or 404 [RFC7231].

Note: Since the CORS protocol is part of a Living Standard, it might be changed at any point, which might necessitate changes to data pod implementations for continued prevention of undesired blocking. A proposal to mitigate this has been suggested.

Concretely, whenever a data pod receives an HTTP request containing a valid Origin header [RFC6454], the server MUST respond with the appropriate Access-Control-* headers as specified in the CORS protocol [FETCH]. In particular, the data pod MUST set the Access-Control-Allow-Origin header to the valid Origin value from the request and list Origin in the Vary header value. The data pod MUST make all used response headers readable for the Solid app through Access-Control-Expose-Headers (with the possible exception of the Access-Control-* headers themselves). A data pod MUST also support the HTTP OPTIONS method [RFC7231] such that it can respond appropriately to CORS preflight requests.

Careful attention is warranted, especially because of the many edge cases. For instance, data pods SHOULD explicitly enumerate all used response headers under Access-Control-Expose-Headers rather than resorting to *, which does not cover all cases (such as credentials mode set to include). Data pods SHOULD also explicitly list Accept under Access-Control-Allow-Headers, because values longer than 128 characters (not uncommon for RDF-based Solid apps) would otherwise be blocked, despite shorter Accept headers being allowed without explicit mention.

Identity

WebID

A WebID is an HTTP URI denoting an agent, for example a person, organisation, or software [WEBID]. When a WebID is dereferenced, server provides a representation of the WebID Profile in an RDF document [RDF11-CONCEPTS] which uniquely describes an agent denoted by a WebID. WebIDs are an underpinning component in the Solid ecosystem and are used as the primary identifier for users and applications.

When using Web Access Control (Web Access Control):

Agents accessing non-public Solid resources need to authenticate with a WebID.

Authentication

Solid-OIDC

The Solid OpenID Connect (Solid OIDC) specification defines how resource servers verify the identity of relying parties and end users based on the authentication performed by an OpenID provider [SOLID-OIDC].

WebID-TLS

This section is non-normative.

The Solid ecosystem initially relied on WebID-TLS for authenticated resource access [WEBID-TLS]. The current recommendation for authentication relies on Solid-OIDC (Solid-OIDC). Implementations can use WebID-TLS just as any other mechanism as an additional authentication method.

Authorization

Web Access Control

Web Access Control (WAC) is a decentralized cross-domain access control system. The WAC mechanism is concerned with giving access to agents denoted by a WebID to perform various kinds of read-write operations on resources identified by URLs. The Access Control List (ACL) ontology is used to describe authorization policies about agents with modes of access on target resources.

Servers MUST conform to the Web Access Control specification [WAC].

A resource can advertise an ACL document that is directly associated by using the HTTP Link header with a rel value of acl acl. [Source]

In the event that a server can’t apply an ACL to a resource, it MUST deny access. [Source]

Servers exposing client’s access privileges on a resource URL MUST advertise by including the WAC-Allow HTTP header in the response of HTTP HEAD and GET requests.

The syntax for the WAC-Allow header, using the ABNF syntax defined in Section 1.2 of [RFC7231], is:

wac-allow        = "WAC-Allow" ":" OWS #access-param OWS
access-param     = permission-group OWS "=" OWS access-modes
permission-group = 1*ALPHA
access-modes     = DQUOTE OWS *1(access-mode *(RWS access-mode)) OWS DQUOTE
access-mode      = "read" / "write" / "append" / "control"

The WAC-Allow HTTP header’s field-value is a comma-separated list of access-params. access-param is a whitespace-separated list of access-modes granted to a permission-group.

This specification defines the following permission-groups:

user
Permissions granted to the agent requesting the resource.
public
Permissions granted to the public.

access-mode corresponds to the modes of access as defined in the ACL ontology (acl:Read, acl:Write, acl:Append, acl:Control).

Clients can discover access privileges on a resource by making an HTTP HEAD or GET request on the target URL, and checking the WAC-Allow header value for access parameters listing the allowed access modes per permission group.

Clients' parsing algorithm for the WAC-Allow header should incorporate error handling. When the received message fails to match an allowed pattern, finds unrecognised access parameters or access modes, clients MUST ignore the received WAC-Allow header-field.

[Source] [Source] Source] Source]

HTTP Definitions

HTTP Headers

The Accept-Put Response Header

This specification introduces a new HTTP response header Accept-Put used to specify the document formats accepted by the server on HTTP PUT requests. It is modelled after the Accept-Patch header defined in [RFC5789] and the Accept-Post header defined in [LDP].

The syntax for Accept-Put, using the ABNF syntax defined in Section 1.2 of [RFC7231], is:

Accept-Put = "Accept-Put" ":" # media-range

The Accept-Put header specifies a comma-separated list of media ranges (with optional parameters) as defined by [RFC7231], Section 5.3.2. The Accept-Put header, in effect, uses the same syntax as the HTTP Accept header minus the optional accept-params BNF production, since the latter does not apply to Accept-Put.

The presence of the Accept-Put header in response to any method is an implicit indication that PUT is allowed on the resource identified by the request URI. The presence of a specific document format in this header indicates that that specific format is allowed on PUT requests to the resource identified by the request URI.

IANA Registration Template:

The Accept-Put response header must be added to the permanent registry (see [RFC3864]).

Header field name
Accept-Put
Applicable Protocol
HTTP
Author/Change controller
W3C Solid Community Group
Specification document
This specification

Considerations

This section details security, privacy, accessibility and internationalization considerations.

Some of the normative references with this specification point to documents with a Living Standard or Draft status, meaning their contents can still change over time. It is advised to monitor these documents, as such changes might have implications.

Security Considerations

This section is non-normative.

While this section attempts to highlight a set of security considerations, it is not a complete list. Implementers are urged to seek the advice of security professionals when implementing mission critical systems using the technology outlined in this specification.

Implementations are subject to the same security considerations that are found in HTTP/1.1 [RFC7230] and [RFC7231].

Servers are strongly discouraged from assuming that HTTP request headers’ field-values are valid or non-malicious. Servers are strongly encouraged to sanitize requests before processing them or incorporating them in messages sent to others. Servers are encouraged to reject bad requests that conflict with this specification's normative requirements. Servers are encouraged to apply normalization and canonicalization algorithms where applicable. Servers are encouraged to take measures to mitigate potential timing attacks attempting to discover resource existence even if requesting agent has no access to the resource(s). Servers are strongly discouraged from exposing information beyond the minimum amount necessary to enable a feature.

Servers are strongly discouraged from assuming that the user agent is a regular Web browser, even when requests contain familiar values in headers such as User-Agent or Origin. Such an assumption could lead to incorrect conclusions about the security model of the application making the request, since the request might actually come from a non-browser actor unaffected by browser security constraints.

Servers disable all cross-origin protections in browsers because resource access is governed explicitly by Web Access Control. As such, servers cannot rely on browser-based cross-origin protection mechanisms for determining the authentication status or representation of a resource. In particular, servers are strongly encouraged to ignore HTTP cookies from untrusted origins. Additional security measures can be taken to prevent metadata in error responses from leaking. For instance, a malicious application could probe multiple servers to check whether the response status code is 401 or 403, or could try to access an error page from an intranet server within the user agent’s private network to extract company names or other data. To mitigate this, when a request from an untrusted Origin arrives, the server may want to set the status code of error responses to 404 and/or anonymize or censor their contents.

Servers are encouraged to use TLS connections to protect the contents of requests and responses from eavesdropping and modification by third parties. Unsecured TCP connections without TLS may be used in testing environments or when the data pod is behind a reverse proxy that terminates a secure connection.

Privacy Considerations

This section is non-normative.

Servers are encouraged to use authorization techniques to prevent unwanted access to resources, rather than depending on the relative obscurity of their resource names.

Identifiable Information

In order to prevent leakage of non-resource data, servers are strongly discouraged from including identifiable information in error responses.

Accessibility Considerations

This section is non-normative.

We acknowledge the diversity of people using the Web, anyone that may create or use information. Our aim is to have inclusive designs for wide range of people and their abilities. This section details general accessibility considerations to take into account for Web content accessibility, accessible applications, authoring tools, and accessible user agents that uses this specification.

Web Content Accessibility: As with implementation of any Web standard or protocol, ignoring accessibility issues makes information unusable by a large subset of the population. It is strongly encouraged to follow accessibility guidelines and standards, such as the W3C Accessibility Guidelines [WCAG-3.0] to cover an array of recommendations to make content accessible to a wider range of people regardless of any disability, limitation, or sensitivity. It is also strongly encouraged to follow the guidance of Making content usable for people with cognitive and learning disabilities [COGA-USABLE].

Accessible Applications: To help assistive technologies to provide a consistent user interface and understanding of the objects, it is strongly encouraged to follow the Accessible Rich Internet Applications [WAI-ARIA-1.2] recommendations. To enable semantic navigation, styling and interactive features in context of digital publishing, it is encouraged to follow the Digital Publishing WAI-ARIA Module 1.0 [DPUB-ARIA-1.0]. To support structured graphics such as charts, graphs, technical drawings and scientific diagrams, to assistive technologies in order improve accessibility of graphics or diagrams through detailed annotations, it is encouraged to follow the WAI-ARIA Graphics Module [GRAPHICS-ARIA-1.0].

Authoring Tool Accessibility: To contribute to the proliferation of Web content that is accessible to a broad range of people, it is strongly encouraged to follow the Authoring Tool Accessibility Guidelines [ATAG20] in the design of authoring tools to support the production of accessible content through accessible user interfaces.

User Agent Accessibility Guidelines: To support the general principles for the development of accessible user agents, ie. any software that retrieves, renders and facilitates end-user interaction with web content, it is strongly encouraged to follow the User Agent Accessibility Guidelines [UAAG20].

Internationalization Considerations

This section is non-normative.

Adaptability of content and software to the needs of target audiences helps towards accessibility. The mechanisms to cater information and interfaces so that people from any culture, region, or language preference can participate better. Towards this end, it is strongly encouraged to apply the recommendations and best practices of W3C Internationalization Activity. For example, content authors can:

  • include links to navigate to different languages of the content;
  • declare the base language of a document, indicate multiple languages and their directional flow – to help with translations;
  • use Unicode character encoding, eg. UTF-8, in data forms and text to ensure correct effects;
  • check and minimise inappropriate cultural bias, and improve translatability;
  • restrict markup use to structure and semantics.

Security and Privacy Review

..

References

Normative References

[FETCH]
Fetch Standard. Anne van Kesteren. WHATWG. Living Standard. URL: https://fetch.spec.whatwg.org/
[JSON-LD11]
JSON-LD 1.1. Gregg Kellogg; Pierre-Antoine Champin; Dave Longley. W3C. 16 July 2020. W3C Recommendation. URL: https://www.w3.org/TR/json-ld11/
[LDN]
Linked Data Notifications. Sarven Capadisli; Amy Guy. W3C. 2 May 2017. W3C Recommendation. URL: https://www.w3.org/TR/ldn/
[LDP]
Linked Data Platform 1.0. Steve Speicher; John Arwe; Ashok Malhotra. W3C. 26 February 2015. W3C Recommendation. URL: https://www.w3.org/TR/ldp/
[RDF-SCHEMA]
RDF Schema 1.1. Dan Brickley; Ramanathan Guha. W3C. 25 February 2014. W3C Recommendation. URL: https://www.w3.org/TR/rdf-schema/
[RDF11-CONCEPTS]
RDF 1.1 Concepts and Abstract Syntax. Richard Cyganiak; David Wood; Markus Lanthaler. W3C. 25 February 2014. W3C Recommendation. URL: https://www.w3.org/TR/rdf11-concepts/
[RFC2119]
Key words for use in RFCs to Indicate Requirement Levels. S. Bradner. IETF. March 1997. Best Current Practice. URL: https://datatracker.ietf.org/doc/html/rfc2119
[RFC3864]
Registration Procedures for Message Header Fields. G. Klyne; M. Nottingham; J. Mogul. IETF. September 2004. Best Current Practice. URL: https://datatracker.ietf.org/doc/html/rfc3864
[RFC3986]
Uniform Resource Identifier (URI): Generic Syntax. T. Berners-Lee; R. Fielding; L. Masinter. IETF. January 2005. Internet Standard. URL: https://datatracker.ietf.org/doc/html/rfc3986
[RFC5023]
The Atom Publishing Protocol. J. Gregorio, Ed.; B. de hOra, Ed.. IETF. October 2007. Proposed Standard. URL: https://datatracker.ietf.org/doc/html/rfc5023
[RFC5789]
PATCH Method for HTTP. L. Dusseault; J. Snell. IETF. March 2010. Proposed Standard. URL: https://httpwg.org/specs/rfc5789.html
[RFC6454]
The Web Origin Concept. A. Barth. IETF. December 2011. Proposed Standard. URL: https://datatracker.ietf.org/doc/html/rfc6454
[RFC6455]
The WebSocket Protocol. I. Fette; A. Melnikov. IETF. December 2011. Proposed Standard. URL: https://datatracker.ietf.org/doc/html/rfc6455
[RFC6892]
The 'describes' Link Relation Type. E. Wilde. IETF. March 2013. Informational. URL: https://datatracker.ietf.org/doc/html/rfc6892
[RFC7230]
Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing. R. Fielding, Ed.; J. Reschke, Ed.. IETF. June 2014. Proposed Standard. URL: https://httpwg.org/specs/rfc7230.html
[RFC7231]
Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content. R. Fielding, Ed.; J. Reschke, Ed.. IETF. June 2014. Proposed Standard. URL: https://httpwg.org/specs/rfc7231.html
[RFC7232]
Hypertext Transfer Protocol (HTTP/1.1): Conditional Requests. R. Fielding, Ed.; J. Reschke, Ed.. IETF. June 2014. Proposed Standard. URL: https://httpwg.org/specs/rfc7232.html
[RFC7233]
Hypertext Transfer Protocol (HTTP/1.1): Range Requests. R. Fielding, Ed.; Y. Lafon, Ed.; J. Reschke, Ed.. IETF. June 2014. Proposed Standard. URL: https://httpwg.org/specs/rfc7233.html
[RFC7234]
Hypertext Transfer Protocol (HTTP/1.1): Caching. R. Fielding, Ed.; M. Nottingham, Ed.; J. Reschke, Ed.. IETF. June 2014. Proposed Standard. URL: https://httpwg.org/specs/rfc7234.html
[RFC7235]
Hypertext Transfer Protocol (HTTP/1.1): Authentication. R. Fielding, Ed.; J. Reschke, Ed.. IETF. June 2014. Proposed Standard. URL: https://httpwg.org/specs/rfc7235.html
[RFC7540]
Hypertext Transfer Protocol Version 2 (HTTP/2). M. Belshe; R. Peon; M. Thomson, Ed.. IETF. May 2015. Proposed Standard. URL: https://httpwg.org/specs/rfc7540.html
[RFC8174]
Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words. B. Leiba. IETF. May 2017. Best Current Practice. URL: https://datatracker.ietf.org/doc/html/rfc8174
[RFC8288]
Web Linking. M. Nottingham. IETF. October 2017. Proposed Standard. URL: https://httpwg.org/specs/rfc8288.html
[SOLID-OIDC]
Solid Protocol. Aaron Coburn; elf Pavlik; Dmitri Zagidulin. W3C Solid Community Group. W3C Editor's Draft. URL: https://solid.github.io/authentication-panel/solid-oidc/
[Turtle]
RDF 1.1 Turtle. Eric Prud'hommeaux; Gavin Carothers. W3C. 25 February 2014. W3C Recommendation. URL: https://www.w3.org/TR/turtle/
[W3C-HTML]
HTML. W3C. 28 January 2021. W3C Recommendation. URL: https://www.w3.org/TR/html/
[WAC]
Web Access Control. W3C Solid Community Group. W3C Editor's Draft. URL: https://solid.github.io/web-access-control-spec/
[WEBARCH]
Architecture of the World Wide Web, Volume One. Ian Jacobs; Norman Walsh. W3C. 15 December 2004. W3C Recommendation. URL: https://www.w3.org/TR/webarch/
[WEBID]
Web Identity and Discovery. W3C Editor's Draft. URL: https://www.w3.org/2005/Incubator/webid/spec/identity/

Informative References

[ATAG20]
Authoring Tool Accessibility Guidelines (ATAG) 2.0. Jan Richards; Jeanne F Spellman; Jutta Treviranus. W3C. 24 September 2015. W3C Recommendation. URL: https://www.w3.org/TR/ATAG20/
[COGA-USABLE]
Making content usable for people with cognitive and learning disabilities. Lisa Seeman-Horwitz; Rachael Bradley Montgomery; Steve Lee; Ruoxi Ran. W3C. 11 December 2020. W3C Working Draft. URL: https://www.w3.org/TR/coga-usable/
[DPUB-ARIA-1.0]
Digital Publishing WAI-ARIA Module 1.0. Matt Garrish; Tzviya Siegman; Markus Gylling; Shane McCarron. W3C. 14 December 2017. W3C Recommendation. URL: https://www.w3.org/TR/dpub-aria-1.0/
[GRAPHICS-ARIA-1.0]
WAI-ARIA Graphics Module. Amelia Bellamy-Royds; Joanmarie Diggs; Michael Cooper. W3C. 2 October 2018. W3C Recommendation. URL: https://www.w3.org/TR/graphics-aria-1.0/
[UAAG20]
User Agent Accessibility Guidelines (UAAG) 2.0. James Allan; Greg Lowney; Kimberly Patch; Jeanne F Spellman. W3C. 15 December 2015. W3C Note. URL: https://www.w3.org/TR/UAAG20/
[WAI-ARIA-1.2]
Accessible Rich Internet Applications (WAI-ARIA) 1.2. Joanmarie Diggs; James Nurthen; Michael Cooper. W3C. 2 March 2021. W3C Candidate Recommendation. URL: https://www.w3.org/TR/wai-aria-1.2/
[WCAG-3.0]
W3C Accessibility Guidelines (WCAG) 3.0. Jeanne F Spellman; Rachael Bradley Montgomery; Shawn Lauriat; Michael Cooper. W3C. 21 January 2021. W3C Working Draft. URL: https://www.w3.org/TR/wcag-3.0/
[WEBID-TLS]
WebID Authentication over TLS. Henry Story; Stéphane Corlosquet; Andrei Sambra. W3C WebID Community Group. W3C Editor's Draft. URL: https://www.w3.org/2005/Incubator/webid/spec/tls/