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<pre class='metadata'>
Title: Solid WebPushSubscription2022
Boilerplate: issues-index no
Local Boilerplate: logo yes
Shortname: solid-webpush-subscription-2022
Level: 1
Status: w3c/ED
Group: Solid Community Group
Favicon: https://solidproject.org/TR/solid.svg
ED: https://solid.github.io/notifications/webpush-subscription-2022
Repository: https://github.com/solid/notifications
Inline Github Issues: title
Markup Shorthands: markdown yes
Max ToC Depth: 2
Editor: [Christoph Braun](https://github.com/uvdsl)
Abstract:
The [[!SOLID-NOTIFICATIONS inline]] defines a set of interaction patterns for agents to establish subscriptions to resources in a Solid Storage.
This specification defines a subscription type that applies these patterns to the [[!PUSH-API inline]].
Status Text:
This section describes the status of this document at the time of its publication.
This document was published by the [Solid Community Group](https://www.w3.org/community/solid/) as
an Editor’s Draft. The information in this document is
still subject to change. You are invited to [contribute](https://github.com/solid/solid-oidc/issues)
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)](https://www.w3.org/community/about/process/cla/). A human-readable
[summary](https://www.w3.org/community/about/process/cla-deed/) is available.
</pre>
<div class="note">
This darft is based on a submission for [Web Push Notifications from Solid Pods](https://uvdsl.solid.aifb.kit.edu/conf/2022/icwe/demo).
<ul>
<li>The submission's server-side (Pod-side) code can be found [here](https://github.com/uvdsl/solid-web-push).</li>
<li>The submission's client-side (PWA-side) code can be found [here](https://github.com/uvdsl/solid-web-pwa).</li>
</ul>
DISCLAIMER: The submission and its implementation may become obsolete with progression of this draft.
</div>
# Introduction # {#introduction}
*This section is non-normative.*
The [[!SOLID-NOTIFICATIONS inline]] describes a general pattern by which agents can be notified when a Solid Resource changes.
This document describes a Solid Notifications subscription type that makes use of the [[!PUSH-API inline]] for Web Push notifications in Progressive Web Applications (PWAs).
This specification is for:
* Resource server developers who wish to enable clients, i.e., PWAs, to listen for updates to particular resources.
* Application developers who wish to implement a client, i.e., a PWA, to listen for updates to particular resources.
## Terminology ## {#terminology}
*This section is non-normative.*
This document uses terminology from the [[!SOLID-NOTIFICATIONS]] protocol,
including "Notification Subscription API".
The document uses terms from the [[!WEBSUB]] specification,
including "topic".
Issue(62):
Note: Let the predicate `topic` be an `rdfs:subClassOf` of `as:object`?
The document further uses terms from [[!PUSH-API]] specification,
including "push endpoint", "push service" and "authentication secret".
It also uses terms from [[!OAUTH-2.0]] specification,
including "authorization server" and "access token".
In addition, the document uses terms from the [[!WEBARCH]] specification,
including "information resource".
This document uses the following terms as defined below:
: subscription service
:: A `subscription service` is a service, which handles and manages subscriptions for resources stored on the corresponding Solid Storage.
:: The `subscription service` is identified by a URI. Dereferencing this URI yields the `subscription service`'s representation, a discription of the service. By this representation, information may be provided such as Notification Subscription APIs where subscriptions can be submitted for the service to process.
Issue(63):
Issue(36):
: browser messaging service
:: Refers to the implementation of a "push service" [[!PUSH-API]] in a browser.
## Overview ## {#overview}
The following diagram shows the high-level interactions involved in this flow.
How a client retrieves an access token is outside the scope of this document.
<figure>
<img src="webpush-subscription-2022-flow.mmd.svg" rel="schema:image" width="800">
<figcaption property="schema:name">Solid WebPushSubscription2022 Flow</figcaption>
</figure>
<ul>
<li>
**Discovery:**
The *subscriber* discovers from the *storage metadata* a suitable *subscription service*.
It further discovers from the *subscription service*'s representation a suitable Notification Subscription API to submit subscription requests to and the `vapidPublicKey` of the *subscription service*.
</li>
<li>
**Establish Subscription:**
The *subscriber* subscribes to the *browser messaging service* to receive Web Push notifications using the `vapidPublicKey` of the *subscription service*.
In return, the *subscriber* retrieves the `endpoint`, `auth` and `p256dh` values.
A corresponding subscription is submitted to the Notification Subscription API.
The *subscription service* authenticates the *subscriber* with the *Authorization Server*, checks authorization of the *subscriber* and registers the subscription.
</li>
<li>
**Deliver Notifications:**
The *subscription service* issues Push notifications to the *browser messaging serivce* which in turn delivers the Push notification to the *subscriber*.
For each notification, the *subscription service* checks the authorization of the *subscriber* with the *Authorization Server*.
</li>
<li>
**Cancel Subscription:**
When the *subscriber* chooses not to receive Web Push notifications anymore, it unsubscribes from the *browser messaging service*.
Additionally, it sends an unsubscription request to the *subscription service*.
</li>
</ul>
<div class="advisement">
<b>
It is not yet specified by [[!SOLID-NOTIFICATIONS]], how unsubscription works. Depends on #36.
</b>
<ul>
<li>
Option (1): `as:Undo` via HTTP POST to Notification Subscription API.
</li>
<li>
Option (2): HTTP DELETE on a subscription.
</li>
</ul>
</div>
# WebPushSubscription2022 Type # {#subscription-type}
This specification defines the WebPushSubscription2022 type for use with Solid Notifications subscriptions.
The URI of the subscription type is <http://www.w3.org/ns/solid/notification#WebPushSubscription2022>.
A WebPushSubscription2022 API MUST conform to the [Solid Notifications Protocol](https://solid.github.io/notifications/protocol#discovery).
A WebPushSubscription2022 API SHOULD support the [Solid Notifications Features](https://solid.github.io/notifications/protocol#notification-features).
Note: Let the class `WebPushSubscription2022` be an `rdfs:subClassOf` of `as:Follow`?
The WebPushSubscription2022 type defines the following properties:
: vapidPublicKey
:: The `vapidPublicKey` property indicates the notification server's public key as defined by [[!RFC8292]], which can be used by the client for the Voluntary Application Server Identification (VAPID).
%% : object
%% :: The `object` property indicates the information resource which the client would like to receive notifications about.
%% The value of source property MUST be a URI, using the `https` scheme, and identifying an information resource.
%% Note: Let the predicate `topic` be an `rdfs:subClassOf` of `as:object`?
%% Issue(62):
: endpoint
:: The `endpoint` property indicates the "Push Endpoint" as defined in the [[!PUSH-API]] specification.
: keys
:: The `keys` property indicates a "cryptographic keys object" that has the properties of `auth` and `p256dh`.
: auth
:: The `auth` property indicates the "authentication secret" as defined in the [[!RFC8291]] specifications.
: p256dh
:: The `p256dh` property indicates the elliptic curve Diffie-Hellman (ECDH) public key as defined by [[!RFC8291]].
A client establishes a subscription using the `WebPushSubscription2022` type
by sending an authenticated subscription request to the `subscriptions service`'s Notification Subscription API retrieved via [[!SOLID-NOTIFICATIONS]] discovery.
The client sends a `HTTP POST` request with a request body to the appropriate `subscription resource`'s Notification Subscription API.
Required information in the request are `type`, `topic`, `endpoint`, `keys` with `auth` and `p256dh`.
If the subscription has been created successfully, the server responds to a client's subscription request with HTTP status code `201 Created`
Issue(36):
## Subscription Example ## {#example}
*This section is non-normative.*
An example `POST` request using a `DPoP` bound access token is below:
<div class=example>
```http
POST /subscribe/
Authorization: DPoP <token>
DPoP: <proof>
Content-Type: text/turtle
```
```turtle
@prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .
@prefix as: <https://www.w3.org/ns/activitystreams#> .
@prefix push: <https://purl.org/solid-web-push/vocab#> .
@prefix notify: <https://www.w3.org/ns/solid/notification#> .
<> a notify:WebPushSubscription2022;
notify:topic <https://uvdsl.solid.aifb.kit.edu/inbox/>;
push:endpoint <https://fcm.googleapis.com/fcm/send/ezblK6NIv80:APA91bHrjqImGaqs5-kcIZ_zO72HVDHGfnrzi9xwJvSsHD3qu4js1nQfHvcjf1Fjgo3mpxBqMkFcqPdiaRPFXnYSkEf9yz78m9FFBaWzwIvmaQ8M1-2vxaAO3S-ha2jf7ALLqRP92Y9z>;
push:keys [
push:auth "Z51Yn6DRglyzR6SpDYHkqw"^^xsd:base64Binary;
push:p256dh "BNocq-WqQufNxY5NtFWz-ckbLoCprrHT74ALR-DXcpCoKmqV2cVflQ6ibyas-vJBMWMLeSDPdRBbJhcc0lDmJ5g"^^xsd:base64Binary
] .
```
Example: POST request creating a `WebPushSubscription2022` subscription.
</div>
%% Note: TODO check data types of `auth` and `p256dh`.
A successful response will have a HTTP status code of `201 Created` and no (meaningful) response body.
The Notification Subscription API, in our example `/subscribe/`, where the POST request is submitted to, is discovered from the *subscription service*'s representation:
<div class=example>
```turtle
# available at <https://solid.aifb.kit.edu/web-push/service>
@prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>.
@prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#>.
@prefix dc: <http://purl.org/dc/terms/>.
@prefix xsd: <http://www.w3.org/2001/XMLSchema#>.
@prefix as: <https://www.w3.org/ns/activitystreams#>.
@prefix ldp: <http://www.w3.org/ns/ldp#>.
@prefix push: <https://purl.org/solid-web-push/vocab#>.
<> a as:Profile;
rdfs:label "The profile of the Solid Web Push Service"@en;
as:summary "The described resource is a Service called Solid Web Push. To subscribe to the service, post the subscription to the provided URI. The subscription must indicate which resource the subscriber whishes to receive updates on.";
dc:creator <https://uvdsl.solid.aifb.kit.edu/profile/card#me>;
as:describes <#web-push> .
<#web-push> a as:Service;
as:name "Solid Web Push"@en;
rdfs:label "Solid Web Push Service"@en;
ldp:inbox <https://solid.aifb.kit.edu/web-push/subscribe/>;
push:vapidPublicKey "BAOxV1U1Hj5npToInct2VhhYpJkL0GmHqc-ADbHu7O8Z2CJNkqSzc8BfCStWbTKq_yT9B6g6kYjyEHrAEpVuqww"^^xsd:base64Binary.
```
Example: Representation of a *subscription service*.
</div>
Note: The representation includes the Notification Subscription API where subscriptions can be submitted via POST using `ldp:inbox`.
Currently, it is not yet specified by [[!SOLID-NOTIFICATIONS]] how the subscription service is modelled.
To this end, the example is my suggestion.
For Unsubscription,
<div class="advisement">
<b>
It is not yet specified by [[!SOLID-NOTIFICATIONS]], how unsubscription works. Depends on #36.
</b>
<ul>
<li>
Option (1): `as:Undo` via HTTP POST to Notification Subscription API.
</li>
<li>
Option (2): HTTP DELETE on a subscription.
</li>
</ul>
</div>
Note: When there is a decision reached, there will be an example included.
# Authentication and Authorization # {#auth}
As described by the Solid Notifications Protocol section on Authorization,
the WebPush subscription API requires authorization and follows the guidance of the Solid Protocol
sections on Authentication and Authorization [[!SOLID-PROTOCOL]].
It is beyond the scope of this document to describe how a client fetches an access token.
Solid-OIDC is one example of an authentication mechanism that could be used with Solid Notifications [[!SOLID-OIDC]].
<pre class=biblio>
{
"SOLID-PROTOCOL": {
"authors": [
"Sarven Capadisli",
"Tim Berners-Lee",
"Ruben Verborgh",
"Kjetil Kjernsmo"
],
"href": "https://solidproject.org/TR/protocol",
"title": "Solid Protocol",
"publisher": "W3C Solid Community Group"
},
"SOLID-NOTIFICATIONS": {
"authors": [
"Aaron Coburn",
"Sarven Capadisli"
],
"href": "https://solid.github.io/notifications/protocol",
"title": "Solid Notifications Protocol",
"publisher": "W3C Solid Community Group"
},
"SOLID-OIDC": {
"authors": [
"Aaron Coburn",
"elf Pavlik",
"Dmitri Zagidulin"
],
"href": "https://solid.github.io/solid-oidc",
"title": "Solid-OIDC",
"publisher": "W3C Solid Community Group"
},
"PUSH-API": {
"authors": [
"Peter Beverloo",
"Martin Thomson"
],
"href": "https://www.w3.org/TR/push-api/",
"title": "Push API",
"publisher": "W3C Web Applications Working Group"
},
"OAUTH-2.0": {
"authors": [
"D. Hardt"
],
"href": "https://www.ietf.org/rfc/rfc6749.txt",
"title": "The OAuth 2.0 Authorization Framework",
"publisher": "Internet Engineering Task Force (IETF)"
},
"WEBSUB": {
"authors": [
"Julien Genestoux",
"Aaron Parecki"
],
"href": "https://www.w3.org/TR/websub/",
"title": "WebSub",
"publisher": "W3C Social Web Working Group"
},
"WEBARCH": {
"authors": [
"Ian Jacobs",
"Norman Walsh"
],
"href": "https://www.w3.org/TR/webarch/",
"title": "Architecture of the World Wide Web, Volume One",
"publisher": "W3C Technical Architecture Group"
},
"RFC8291": {
"authors": [
"M. Thomson"
],
"href": "https://www.ietf.org/rfc/rfc8291.txt",
"title": "Message Encryption for Web Push",
"publisher": "Internet Engineering Task Force (IETF)"
},
"RFC8292": {
"authors": [
"M. Thomson",
"P. Beverloo"
],
"href": "https://www.ietf.org/rfc/rfc8292.txt",
"title": "Voluntary Application Server Identification (VAPID) for Web Push",
"publisher": "Internet Engineering Task Force (IETF)"
}
}
</pre>