Status of This DocumentThis document is an incomplete 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.
Write Introduction section.
Explain the principle of orthogonality, by which this spec is split into multiple documents.
Explain that this specification is not documentation; it is the easiest way to understand how Solid works, not the easiest way for building a Solid app.
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.
Introduce the structure of this document. Cross-server interoperability Cross-app interoperability
2. Authenticated Resource Access
Write introduction to the Authenticated Resource Access section.
2.1. Hypertext Transfer Protocol
2.1.1. Background and NeedThis section is non-normative.
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.
2.1.2. 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
https URI scheme
in order to secure the communication between clients and servers.
https are supported,
http URIs MUST redirect to their
using a response with a
301 status code and a
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 § 2.3 WebID),
the data pod MUST send a response with a
401 status code
404 is preferred for security reasons).
2.1.3. 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 § 2.3 WebID).
When it receives a response with a
404 status code,
it MAY repeat the request with different credentials.
2.2. Linked Data Platform
Write Linked Data Platform section.
Draft: A Solid data pod MUST conform to the LDP specification [LDP].
Explain inline that agents accessing non-public Solid resources need to authenticate with a WebID, which is a URL pointing to a document with an RDF representation.
Write WebID-OIDC section.
Draft: A Solid data pod MUST conform to the WebID-OIDC specification [WEBID-OIDC].
Write WebID-TLS section.
Draft: A Solid data pod MAY conform to the WebID-TLS specification [WEBID-TLS].
2.4. Web Access Control
Write Web Access Control section.
Draft: A Solid data pod MUST conform to the Web Access Control specification [WAC].
2.5. Cross-Origin Resource Sharing
2.5.1. Background and NeedThis section is non-normative.
Solid apps typically access data from multiple sources.
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.
a Solid app at
https://app.example/ would be prevented from accessing data on
even when Alice and Bob 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—
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.
2.5.2. 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
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.
whenever a data pod receives an HTTP request
containing a valid
Origin header [RFC6454],
the server MUST respond with the appropriate
as specified in the CORS protocol [FETCH].
the data pod MUST set the
to the valid
Origin value from the request
Origin in the
Vary header value.
The data pod MUST make all used response headers readable for the Solid app
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.
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
Data pods SHOULD also explicitly list
because values longer than 128 characters
(not uncommon for RDF-based Solid apps)
would otherwise be blocked,
Accept headers being allowed without explicit mention.
3. Clients and Apps
Write introduction to the Clients and Apps section.
3.1. Implementation GuidanceThis section is non-normative.
Write Implementation Guidance section.
3.2. Data Shapes and Footprints
Write introduction to Data Shapes and Footprints section.
3.2.1. Data Shapes
Write Data Shapes section.
Draft: A Solid client MUST conform to the SHACL specification [SHACL].
SHACL or ShEx?
Write Footprints section.
Draft: A Solid client MUST conform to the Data Footprints specification [FOOTPRINTS].
3.3. Data Shape GuidanceThis section is non-normative.
Write Data Shape Guidance section.
3.4. Update Notifications
Write Update Notification section.
Draft: A Solid client MUST conform to the LDN specification [LDN].
4. Optional Integrations
Write introduction to the Optional Integrations section.
4.1. Pod and User Management
Write Pod and User Management section.
Draft: A Solid data pod MAY conform to the Pod Management specification [POD-MANAGEMENT].
4.2. Query Interfaces
Write Query Interfaces section.
Draft: A Solid data pod MAY conform to the Triple Pattern Fragments specification [TPF].
4.3. Additional Content Negotiation Dimensions
Write Additional Content Negotiation Dimension section.
Write Memento section.
Draft: A Solid data pod MAY conform to the Memento specification [RFC7089].
Write Profiles section.
Draft: A Solid data pod MAY conform to the Profile-based Content Negotiation specification [PROFILES].
4.4. Verifiable Credentials
Write Verifiable Credentials section.
Draft: A Solid data pod MAY conform to the Verifiable Credentials specification [VERIFIABLE-CREDENTIALS].
5. Security Considerations
Some of the normative references with this specification point to documents with a Living Standard status, meaning their contents can still change over time. It is advised to monitor these documents, as such changes might have security implications.
A data pod MUST NOT assume that
HTTP request headers sent by a client are valid,
and MUST reject or sanitize invalid header values
before processing them
or incorporating them in messages sent to others.
Origin MUST NOT be assumed to be free of possibly malicious sequences
/.. or others,
MUST NOT be echoed into the
Access-Control-Allow-Origin response header.
A data pod MUST NOT assume that the user agent is a regular Web browser,
even when requests contain familiar values
in headers such as
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.
Solid data pods disable all cross-origin protections in browsers
because resource access is governed explicitly by Web Access Control.
data pods MUST NOT rely on browser-based cross-origin protection mechanisms
for determining the authentication status or representation of a resource.
they MUST ignore HTTP cookies from untrusted origins.
Additional security measures MAY be taken
to prevent metadata in error responses from leaking.
a malicious app could probe multiple servers
to check whether the response status code is
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
the data pod MAY set the status code of error responses to
404 and/or anonymize or censor their contents.
Data pods SHOULD 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.
5.1. Privacy Considerations
Write Privacy Considerations section.
5.1.1. Identifiable Information
Write Identifiable Information section.
In order to prevent leakage of non-resource data, error responses SHOULD NOT contain identifiable information.