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<!DOCTYPE html>
<html>
<head>
<title>ActivityPub</title>
<meta charset="utf-8">
<script src="https://www.w3.org/Tools/respec/respec-w3c"
async class="remove"></script>
<script class="remove">
var respecConfig = {
specStatus: "CG-FINAL",
publishDate: "2024-01-04",
previousPublishDate: "2018-01-23",
previousMaturity: "REC",
license: "w3c-software-doc",
shortName: "activitypub",
group: "socialcg",
wgURI: "https://www.w3.org/Social/WG",
wgPublicList: "public-socialweb",
wgPatentURI: "https://www.w3.org/2004/01/pp-impl/72531/status",
edDraftURI: "https://w3c.github.io/activitypub/",
testSuiteURI: "https://test.activitypub.rocks/",
errata: "https://www.w3.org/wiki/ActivityPub_errata",
implementationReportURI: "https://activitypub.rocks/implementation-report",
otherLinks: [
{
"key": "Repository",
"data": [
{
"value": "Git repository",
"href": "https://github.com/w3c/activitypub",
},
{
"value": "Issues",
"href": "https://github.com/w3c/activitypub/issues",
},
{
"value": "Commits",
"href": "https://github.com/w3c/activitypub/commits/gh-pages",
}
]
}
],
editors: [
{
name: "Christopher Lemmer Webber",
url: "https://dustycloud.org/",
w3cid: "57007"
},
{
name: "Jessica Tallon",
url: "https://tsyesika.se",
w3cid: "72695"
},
],
authors: [
{
name: "Christopher Lemmer Webber",
url: "https://dustycloud.org/"
},
{
name: "Jessica Tallon",
url: "https://tsyesika.se"
},
{
name: "Erin Shepherd",
url: "http://erinshepherd.net/"
},
{
name: "Amy Guy",
url: "https://rhiaro.co.uk/"
},
{
name: "Evan Prodromou",
url: "https://en.wikipedia.org/wiki/Evan_Prodromou"
}
],
localBiblio: {
"ActivityStreams": {
title: "Activity Streams 2.0",
href: "https://www.w3.org/TR/activitystreams-core/",
authors: [
"J. Snell",
],
status: "Editors Draft",
publisher: "ActivityStreams Working Group",
},
"Activity-Vocabulary": {
title: "Activity Vocabulary",
href: "https://www.w3.org/TR/activitystreams-vocabulary/",
authors: [
"J. Snell",
],
status: "Editors Draft",
publisher: "ActivityStreams Working Group",
},
"OAuth-Server-Metadata": {
title: "OAuth 2.0 Authorization Server Metadata",
href: "https://tools.ietf.org/html/draft-ietf-oauth-discovery-06",
authors: [
"M. Jones",
"N. Sakimura",
"J. Bradley"
],
status: "Internet-Draft",
publisher: "OAuth Working Group",
},
},
};
</script>
<style type="text/css">
img {
max-width: 100%;
}
</style>
</head>
<!-- STYLISTIC NOTE: This document wraps on column 79 and at the end of every
sentence. -->
<body>
<section id="abstract">
<p>
The ActivityPub protocol is a decentralized social networking protocol
based upon the [[ActivityStreams]] 2.0 data format.
It provides a client to server API for creating, updating and deleting
content, as well as a federated server to server API for delivering
notifications and content.
</p>
</section>
<section id="sotd">
</section>
<section id="Overview">
<h2>Overview</h2>
<p>ActivityPub provides two layers:</p>
<ul>
<li>
<b>A server to server federation protocol</b>
(so decentralized websites can share information)
</li>
<li>
<b>A client to server protocol</b>
(so users, including real-world users, bots, and other automated processes,
can communicate with ActivityPub using their accounts on servers,
from a phone or desktop or web application or whatever)
</li>
</ul>
<p>
ActivityPub implementations can implement just one of these things or
both of them.
However, once you've implemented one, it isn't too many steps to
implement the other, and there are a lot of benefits to both (making
your website part of the decentralized social web, and being able to
use clients and client libraries that work across a wide variety of
social websites).
</p>
<p>
In ActivityPub, a user is represented by "<a href="#actors">actors</a>"
via the user's accounts on servers.
User's accounts on different servers correspond to different actors.
Every Actor has:
</p>
<ul>
<li><b>An <code>inbox</code>:</b> How they get messages from the world</li>
<li><b>An <code>outbox</code>:</b> How they send messages to others</li>
</ul>
<p>
<img src="illustration/tutorial-1.png"
alt="Actor with inbox and outbox" />
</p>
<p>
These are endpoints, or really, just URLs which are listed in the
ActivityPub actor's ActivityStreams description.
(More on ActivityStreams later).
</p>
<p>
Here's an example of the record of our friend Alyssa P. Hacker:
</p>
<pre class="example highlight json">
{"@context": "https://www.w3.org/ns/activitystreams",
"type": "Person",
"id": "https://social.example/alyssa/",
"name": "Alyssa P. Hacker",
"preferredUsername": "alyssa",
"summary": "Lisp enthusiast hailing from MIT",
"inbox": "https://social.example/alyssa/inbox/",
"outbox": "https://social.example/alyssa/outbox/",
"followers": "https://social.example/alyssa/followers/",
"following": "https://social.example/alyssa/following/",
"liked": "https://social.example/alyssa/liked/"}
</pre>
<p>
ActivityPub uses [[!ActivityStreams]] for its vocabulary.
This is pretty great because ActivityStreams includes all the common
terms you need to represent all the activities and content flowing
around a social network.
It's likely that ActivityStreams already includes all the vocabulary
you need, but even if it doesn't, ActivityStreams can be extended
via [[!JSON-LD]].
If you know what JSON-LD is, you can take advantage of the cool linked
data approaches provided by JSON-LD.
If you don't, don't worry, JSON-LD documents and ActivityStreams can be
understood as plain old simple JSON.
(If you're going to add extensions, that's the point at which JSON-LD
really helps you out).
</p>
<p>
So, okay.
Alyssa wants to talk to her friends, and her friends want to talk to
her!
Luckily these "inbox" and "outbox" things can help us out.
They both behave differently for GET and POST.
Let's see how that works:
</p>
<p>
<img src="illustration/tutorial-2.png"
alt="Actor with messages flowing from rest of world to inbox and from outbox to rest of world" />
</p>
<p>
Hey nice, so just as a recap:
</p>
<ul>
<li>
You can POST to someone's inbox to send them a message
(server-to-server / federation only... this <em>is</em> federation!)
</li>
<li>
You can GET from your inbox to read your latest messages
(client-to-server; this is like reading your social
network stream)
</li>
<li>
You can POST to your outbox to send messages to the world
(client-to-server)
</li>
<li>
You can GET from someone's outbox to see what messages they've
posted (or at least the ones you're authorized to see).
(client-to-server and/or server-to-server)
</li>
</ul>
<p>
Of course, if that last one (GET'ing from someone's outbox) was the
only way to see what people have sent, this wouldn't be a very
efficient federation protocol!
Indeed, federation happens usually by servers posting messages sent by
actors to actors on other servers' inboxes.
</p>
<p>
Let's see an example!
Let's say Alyssa wants to catch up with her friend, Ben Bitdiddle.
She lent him a book recently and she wants to make sure he returns it
to her.
Here's the message she composes, as an ActivityStreams object:
</p>
<pre class="example highlight json">
{"@context": "https://www.w3.org/ns/activitystreams",
"type": "Note",
"to": ["https://chatty.example/ben/"],
"attributedTo": "https://social.example/alyssa/",
"content": "Say, did you finish reading that book I lent you?"}
</pre>
<p>
This is a note addressed to Ben.
She POSTs it to her outbox.
</p>
<p>
<img src="illustration/tutorial-3.png"
alt="Actor posting message to outbox" />
</p>
<p>
Since this is a non-activity object, the server recognizes that this is
an object being newly created, and does the courtesy of wrapping it in
a Create activity.
(Activities sent around in ActivityPub generally follow the pattern of
some activity by some actor being taken on some object.
In this case the activity is a Create of a Note object, posted by a
Person).
</p>
<pre class="example highlight json">
{"@context": "https://www.w3.org/ns/activitystreams",
"type": "Create",
"id": "https://social.example/alyssa/posts/a29a6843-9feb-4c74-a7f7-081b9c9201d3",
"to": ["https://chatty.example/ben/"],
"actor": "https://social.example/alyssa/",
"object": {"type": "Note",
"id": "https://social.example/alyssa/posts/49e2d03d-b53a-4c4c-a95c-94a6abf45a19",
"attributedTo": "https://social.example/alyssa/",
"to": ["https://chatty.example/ben/"],
"content": "Say, did you finish reading that book I lent you?"}}
</pre>
<p>
Alyssa's server looks up Ben's ActivityStreams actor object, finds his
inbox endpoint, and POSTs her object to his inbox.
</p>
<p>
<img src="illustration/tutorial-4.png"
alt="Server posting to remote actor's inbox" />
</p>
<p>
Technically these are two separate steps... one is client to server
communication, and one is server to server communication (federation).
But, since we're using them both in this example, we can abstractly
think of this as being a streamlined submission from outbox to inbox:
</p>
<p>
<img src="illustration/tutorial-5.png"
alt="Note flowing from one actor's outbox to other actor's inbox" />
</p>
<p>
Cool!
A while later, Alyssa checks what new messages she's gotten.
Her phone polls her inbox via GET, and amongst a bunch of cat videos
posted by friends and photos of her nephew posted by her sister, she
sees the following:
</p>
<pre class="example highlight json">
{"@context": "https://www.w3.org/ns/activitystreams",
"type": "Create",
"id": "https://chatty.example/ben/p/51086",
"to": ["https://social.example/alyssa/"],
"actor": "https://chatty.example/ben/",
"object": {"type": "Note",
"id": "https://chatty.example/ben/p/51085",
"attributedTo": "https://chatty.example/ben/",
"to": ["https://social.example/alyssa/"],
"inReplyTo": "https://social.example/alyssa/posts/49e2d03d-b53a-4c4c-a95c-94a6abf45a19",
"content": "<p>Argh, yeah, sorry, I'll get it back to you tomorrow.</p>
<p>I was reviewing the section on register machines,
since it's been a while since I wrote one.</p>"}}
</pre>
<p>Alyssa is relieved, and likes Ben's post:</p>
<pre class="example highlight json">
{"@context": "https://www.w3.org/ns/activitystreams",
"type": "Like",
"id": "https://social.example/alyssa/posts/5312e10e-5110-42e5-a09b-934882b3ecec",
"to": ["https://chatty.example/ben/"],
"actor": "https://social.example/alyssa/",
"object": "https://chatty.example/ben/p/51086"}
</pre>
<p>
She POSTs this message to her outbox.
(Since it's an activity, her server knows it doesn't need to wrap it in
a Create object).
</p>
<p>
Feeling happy about things, she decides to post a public message to her
followers.
Soon the following message is blasted to all the members of her
followers collection, and since it has the special Public group
addressed, is generally readable by anyone.
</p>
<pre class="example highlight json">
{"@context": "https://www.w3.org/ns/activitystreams",
"type": "Create",
"id": "https://social.example/alyssa/posts/9282e9cc-14d0-42b3-a758-d6aeca6c876b",
"to": ["https://social.example/alyssa/followers/",
"https://www.w3.org/ns/activitystreams#Public"],
"actor": "https://social.example/alyssa/",
"object": {"type": "Note",
"id": "https://social.example/alyssa/posts/d18c55d4-8a63-4181-9745-4e6cf7938fa1",
"attributedTo": "https://social.example/alyssa/",
"to": ["https://social.example/alyssa/followers/",
"https://www.w3.org/ns/activitystreams#Public"],
"content": "Lending books to friends is nice. Getting them back is even nicer! :)"}}
</pre>
<section id="social-web-working-group" inlist="" rel="schema:hasPart"
resource="#social-web-working-group">
<h3 property="schema:name">Social Web Working Group</h3>
<div datatype="rdf:HTML" property="schema:description">
<p>
<a href="#Overview">ActivityPub</a> is one of several related
specifications being produced by the Social Web Working Group.
Implementers interested in alternative approaches and complementary
protocols should review [[Micropub]] and the overview document
[[Social-Web-Protocols]].
</p>
</div>
</section>
</section>
<section id="conformance">
<section id="specification-profiles">
<h2>Specification Profiles</h2>
<p>
This specification defines two closely related and interacting
protocols:
</p>
<dl>
<dt>A client to server protocol, or "Social API"</dt>
<dd>
This protocol permits a client to act <i>on behalf</i> of a user.
For example, this protocol is used by a mobile phone application to
interact with a social stream of the user's actor.
</dd>
<dt>A server to server protocol, or "Federation Protocol"</dt>
<dd>
This protocol is used to distribute activities between actors on
different servers, tying them into the same social graph.
</dd>
</dl>
<p>
The ActivityPub specification is designed so that once either of
these protocols are implemented, supporting the other is of very
little additional effort.
However, servers may still implement one without the other.
This gives three conformance classes:
</p>
<dl>
<dt>ActivityPub conformant Client</dt>
<dd>
This designation applies to any implementation of the entirety of the
client portion of the client to server protocol.
</dd>
<dt>ActivityPub conformant Server</dt>
<dd>
This designation applies to any implementation of the entirety of the
server portion of the client to server protocol.
</dd>
<dt>ActivityPub conformant Federated Server</dt>
<dd>
This designation applies to any implementation of the entirety of
the federation protocols.
</dd>
</dl>
<p>
It is called out whenever a portion of the specification only applies
to implementation of the federation protocol.
In addition, whenever requirements are specified, it is called out
whether they apply to the client or server (for the client-to-server
protocol) or whether referring to a sending or receiving server in
the server-to-server protocol.
</p>
</section>
</section>
<section id="obj">
<h2>Objects</h2>
<p>
Objects are the core concept around which both [[!ActivityStreams]] and
ActivityPub are built.
Objects are often wrapped in Activities and are contained in streams of
Collections, which are themselves subclasses of Objects.
See the [[!Activity-Vocabulary]] document, particularly the
<a href="https://www.w3.org/TR/activitystreams-vocabulary/#types">Core Classes</a>;
ActivityPub follows the mapping of this vocabulary very closely.
</p>
<p>
ActivityPub defines some terms in addition to those provided by
ActivityStreams.
These terms are provided in the ActivityPub
<a href="http://www.w3.org/TR/json-ld/#the-context">JSON-LD context</a>
at
<code>https://www.w3.org/ns/activitystreams</code>.
Implementers SHOULD include the ActivityPub context in their
object definitions.
Implementers MAY include additional context as appropriate.
</p>
<p>
ActivityPub shares the same
<a href="https://www.w3.org/TR/activitystreams-core/#urls">
URI / IRI conventions as in ActivityStreams</a>.
</p>
<p>
Servers SHOULD validate the content they receive to avoid content
spoofing attacks.
(A server should do something at least as robust as checking that
the object appears as received at its origin, but mechanisms
such as checking signatures would be better if available).
No particular mechanism for verification is authoritatively specified by
this document, but please see <a href="#security-considerations">Security
Considerations</a> for some suggestions and good practices.
</p>
<div class="informative">
As an example, if example.com receives the activity
<pre class="example">
{
"@context": "https://www.w3.org/ns/activitystreams",
"type": "Like",
"actor": "https://example.net/~mallory",
"to": ["https://hatchat.example/sarah/",
"https://example.com/peeps/john/"],
"object": {
"@context": {"@language": "en"},
"id": "https://example.org/~alice/note/23",
"type": "Note",
"attributedTo": "https://example.org/~alice",
"content": "I'm a goat"
}
}
</pre>
it should dereference the <code>id</code> both to ensure that it exists
and is a valid object, and that it is not misrepresenting the object.
(In this example, Mallory could be spoofing an object allegedly posted
by Alice).
</div>
<section id="obj-id">
<h2>Object Identifiers</h2>
<p>
All Objects in [[!ActivityStreams]] should have unique global
identifiers.
ActivityPub extends this requirement; all objects distributed by the
ActivityPub protocol MUST have unique global identifiers, unless they
are intentionally transient (short lived activities that are not
intended to be able to be looked up, such as some kinds of chat
messages or game notifications).
These identifiers must fall into one of the following groups:
</p>
<ol>
<li>
Publicly dereferencable URIs, such as HTTPS URIs, with their
authority belonging to that of their originating server.
(Publicly facing content SHOULD use HTTPS URIs).
</li>
<li>
An ID explicitly specified as the JSON <code>null</code> object,
which implies an anonymous object (a part of its parent context)
</li>
</ol>
<p>
Identifiers MUST be provided for activities posted in server to
server communication, unless the activity is intentionally transient.
However, for client to server communication, a server receiving an
object posted to the outbox with no specified <code>id</code> SHOULD
allocate an object ID in the actor's namespace and attach it to the
posted object.
</p>
<p>All objects have the following properties:</p>
<dl>
<dt>id</dt>
<dd>
The object's unique global identifier (unless the object is transient,
in which case the <code>id</code> MAY be omitted).
</dd>
<dt>type</dt>
<dd>
The type of the object.
</dd>
</dl>
</section>
<section id="retrieving-objects">
<h2>Retrieving objects</h2>
<p>
The HTTP GET method may be dereferenced against an object's
<code>id</code> property to retrieve the activity.
Servers MAY use HTTP content negotiation as defined in [[!RFC7231]] to
select the type of data to return in response to a request,
but MUST present the ActivityStreams object representation
in response to
<code>application/ld+json; profile="https://www.w3.org/ns/activitystreams"</code>,
and SHOULD also present the ActivityStreams representation in
response to <code>application/activity+json</code> as well.
The client MUST specify an <code>Accept</code> header with the
<code>application/ld+json; profile="https://www.w3.org/ns/activitystreams"</code>
media type in order to retrieve the activity.
</p>
<p>
Servers MAY implement other behavior for requests which do not comply
with the above requirement.
(For example, servers may implement additional legacy protocols, or
may use the same URI for both HTML and ActivityStreams
representations of a resource).
</p>
<p>
Servers MAY require authorization as specified in
<a href="#authorization"></a>, and may additionally implement their
own authorization rules.
Servers SHOULD fail requests which do not pass their authorization
checks with the appropriate HTTP error code, or the 403 Forbidden
error code where the existence of the object is considered private.
An origin server which does not wish to disclose the existence of
a private target MAY instead respond with a status code of
404 Not Found.
</p>
</section>
<section id="source-property">
<h2>The source property</h2>
<p>
In addition to all the properties defined by the
[[!Activity-Vocabulary]], ActivityPub extends the <code>Object</code> by
supplying the <code>source</code> property.
The <code>source</code> property is intended to convey some
sort of source from which the <code>content</code> markup
was derived, as a form of provenance, or to support future
editing by clients.
In general, clients do the conversion from <code>source</code>
to <code>content</code>, not the other way around.
</p>
<p>
The value of <code>source</code> is itself an object
which uses its own <code>content</code> and <code>mediaType</code>
fields to supply source information.
</p>
<pre class="example">
{
"@context": ["https://www.w3.org/ns/activitystreams",
{"@language": "en"}],
"type": "Note",
"id": "http://postparty.example/p/2415",
"content": "<p>I <em>really</em> like strawberries!</p>",
"source": {
"content": "I *really* like strawberries!",
"mediaType": "text/markdown"}
}
</pre>
<div class="note"
title="What to do when clients can't meaningfully handle a mediaType?">
<p>
In general, it's best to let a user edit their original post
in the same source format they originally composed it in.
But not all clients can reliably provide a nice interface for
all source types, and since clients are expected to do the
conversion from <code>source</code> to <code>content</code>,
some clients may work with a media type that another client
does not know how to work with.
While a client could feasibly provide the <code>content</code>
markup to be edited and ignore the source, this means that the
user will lose the more desirable form of the original
<code>source</code> in any future revisions.
A client doing so should thus provide a minimally obtrusive warning
cautioning that the original source format is not understood and is
thus being ignored.
</p>
<p>
For example, Alyssa P. Hacker likes to post to her ActivityPub
powered blog via an Emacs client she has written, leveraging
<a href="http://orgmode.org/">Org mode</a>.
Later she switches to editing on her phone's client, which
has no idea what <code>text/x-org</code> is or how to render
it to HTML, so it provides a text box to edit the original
<code>content</code> instead.
A helpful warning displays above the edit area saying,
"This was originally written in another markup language we don't
know how to handle. If you edit, you'll lose your original
source!"
Alyssa decides the small typo fix isn't worth losing her nice
org-mode markup and decides to make the update when she gets
home.
</p>
</div>
</section>
</section>
<section id="actors">
<h2>Actors</h2>
<p>
ActivityPub actors are generally one of the
<a href="https://www.w3.org/TR/activitystreams-vocabulary/#actor-types">
ActivityStreams Actor Types</a>,
but they don't have to be. For example, a
<a href="https://www.w3.org/TR/activitystreams-vocabulary/#dfn-profile">
Profile</a> object
might be used as an actor, or a type from an ActivityStreams extension.
Actors are <a href="#retrieving-objects">retrieved</a> like any other
Object in ActivityPub.
Like other ActivityStreams objects, actors have an <code>id</code>,
which is a URI.
When entered directly into a user interface (for example on a login
form), it is desirable to support simplified naming.
For this purpose, ID normalization SHOULD be performed as follows:
</p>
<ol>
<li>
If the entered ID is a valid URI, then it is to be used directly.
</li>
<li>
If it appears that the user neglected to add a scheme for a URI that
would otherwise be considered valid, such as
<code>example.org/alice/</code>, clients MAY attempt to provide
a default scheme, preferably <code>https</code>.
</li>
<li>
Otherwise, the entered value should be considered invalid.
</li>
</ol>
<p>
Once the actor's URI has been identified, it should be dereferenced.
</p>
<div class="note">
ActivityPub does not dictate a specific relationship between
"users" and Actors; many configurations are possible.
There may be multiple human users or organizations controlling an
Actor, or likewise one human or organization may control multiple
Actors. Similarly, an Actor may represent a piece of software,
like a bot, or an automated process.
More detailed "user" modelling, for example linking together of Actors which
are controlled by the same entity, or allowing one Actor to be presented
through multiple alternate profiles or aspects, are at the discretion
of the implementation.
</div>
<section id="actor-objects">
<h2><i>Actor</i> objects</h2>
<p>
Actor objects MUST have, in addition to the properties mandated by
<a href="#obj-id"></a>, the following properties:
</p>
<dl>
<dt id="inbox-property">inbox</dt>
<dd>
A reference to an [[!ActivityStreams]]
<a href="https://www.w3.org/TR/activitystreams-vocabulary/#dfn-orderedcollection">
<code>OrderedCollection</code></a>
comprised of all the messages received by the actor; see
<a href="#inbox"></a>.
</dd>
<dt id="outbox-property">outbox</dt>
<dd>
An [[!ActivityStreams]]
<a href="https://www.w3.org/TR/activitystreams-vocabulary/#dfn-orderedcollection">
<code>OrderedCollection</code></a>
comprised of all the messages produced by the actor; see
<a href="#outbox"></a>.
</dd>
</dl>
<p>
Implementations SHOULD, in addition, provide the following
properties:
</p>
<dl>
<dt id="following-property">following</dt>
<dd>
A link to an [[!ActivityStreams]] collection of the actors that
this actor is following; see <a href="#following"></a>
</dd>
<dt id="followers-property">followers</dt>
<dd>
A link to an [[!ActivityStreams]] collection of the actors that
follow this actor; see <a href="#followers"></a>.
</dd>
</dl>
<p>
Implementations MAY provide the following properties:
</p>
<dl>
<dt id="liked-property">liked</dt>
<dd>
A link to an [[!ActivityStreams]] collection of objects this
actor has liked; see <a href="#liked"></a>.
</dd>
</dl>
<pre class="example">
{
"@context": ["https://www.w3.org/ns/activitystreams",
{"@language": "ja"}],
"type": "Person",
"id": "https://kenzoishii.example.com/",
"following": "https://kenzoishii.example.com/following.json",
"followers": "https://kenzoishii.example.com/followers.json",
"liked": "https://kenzoishii.example.com/liked.json",
"inbox": "https://kenzoishii.example.com/inbox.json",
"outbox": "https://kenzoishii.example.com/feed.json",
"preferredUsername": "kenzoishii",
"name": "石井健蔵",
"summary": "この方はただの例です",
"icon": [
"https://kenzoishii.example.com/image/165987aklre4"
]
}
</pre>
<p>Implementations MAY, in addition, provide the following properties:</p>
<dl>
<dt id="streams-property">streams</dt>
<dd>
A list of supplementary Collections which may be of interest.
</dd>
<dt id="preferredUsername">preferredUsername</dt>
<dd>
A short username which may be used to refer to the actor, with no
uniqueness guarantees.
</dd>
<dt id="endpoints">endpoints</dt>
<dd>
A json object which maps additional (typically server/domain-wide)
endpoints which may be useful either for this actor or someone
referencing this actor.
This mapping may be nested inside the actor document as the value
or may be a link to a JSON-LD document with these properties.
</dd>
</dl>
<p>
The <code>endpoints</code> mapping MAY include the following
properties:
</p>
<dl>
<dt id="proxyUrl">proxyUrl</dt>
<dd>
Endpoint URI so this actor's clients may access remote
ActivityStreams objects which require authentication to access.
To use this endpoint, the client posts an
<code>x-www-form-urlencoded</code> <code>id</code> parameter
with the value being the <code>id</code> of the requested
ActivityStreams object.
</dd>
<dt id="oauthAuthorizationEndpoint">oauthAuthorizationEndpoint</dt>
<dd>
If OAuth 2.0 bearer tokens [[RFC6749]] [[RFC6750]] are being used
for authenticating
<a href="#client-to-server-interactions">client to server
interactions</a>,
this endpoint specifies a URI at which a browser-authenticated user
may obtain a new authorization grant.
</dd>
<dt id="oauthTokenEndpoint">oauthTokenEndpoint</dt>
<dd>
If OAuth 2.0 bearer tokens [[RFC6749]] [[RFC6750]] are being used
for authenticating
<a href="#client-to-server-interactions">client to server
interactions</a>,
this endpoint specifies a URI at which a client may acquire an
access token.
</dd>
<dt id="provideClientKey">provideClientKey</dt>
<dd>
If Linked Data Signatures and HTTP Signatures are being used for
authentication and authorization, this endpoint specifies a URI at
which browser-authenticated users may authorize a client's public
key for
<a href="#client-to-server-interactions">client to server
interactions</a>.
</dd>
<dt id="signClientKey">signClientKey</dt>
<dd>
If Linked Data Signatures and HTTP Signatures are being used for
authentication and authorization, this endpoint specifies a URI at
which a client key may be signed by the actor's key for a time
window to act on behalf of the actor in interacting with foreign
servers.
</dd>
<dt id="sharedInbox">sharedInbox</dt>
<dd>
An optional endpoint
<a href="#shared-inbox-delivery">
used for wide delivery of publicly addressed activities
and activities sent to followers</a>.
<code>sharedInbox</code> endpoints SHOULD also be publicly
readable <code>OrderedCollection</code> objects containing
objects addressed to the <a href="#public-addressing">Public</a>
special collection.
Reading from the <code>sharedInbox</code> endpoint MUST NOT present
objects which are not addressed to the <code>Public</code>
endpoint.
</dd>
</dl>
<div class="note" id="as2-actor-properties">
<p>
As the upstream vocabulary for ActivityPub, any applicable
[[!ActivityStreams]] property may be used on ActivityPub Actors.
Some ActivityStreams properties are particularly worth highlighting
to demonstrate how they are used in ActivityPub implementations.
</p>
<dl>
<dt id="url-property">url</dt>
<dd>
A link to the actor's "profile web page", if not equal to the
value of <code>id</code>.
</dd>
<dt id="name-property">name</dt>
<dd>
The preferred "nickname" or "display name" of the actor.
</dd>
<dt id="summary-property">summary</dt>
<dd>A quick summary or bio by the user about themselves.</dd>
<dt id="icon-property">icon</dt>
<dd>
A link to an image or an Image object which represents the user's
profile picture (this may be a thumbnail).
</dd>
</dl>
</div>
<p class="note" id="actor-text-direction">
Properties containing natural language values,
such as <code>name</code> or
<code>summary</code>, make use of
<a href="https://www.w3.org/TR/activitystreams-core/#naturalLanguageValues">
natural language support defined in ActivityStreams</a>.
</p>
</section>
</section>
<section id="collections">
<h2>Collections</h2>
<p>
[[!ActivityStreams]] defines the collection concept; ActivityPub
defines several collections with special behavior.
Note that ActivityPub makes use of
<a href="https://www.w3.org/TR/activitystreams-core/#paging">
ActivityStreams paging</a>
to traverse large sets of objects.
</p>
<p>
Note that some of these collections are specified to be of type
<a href="https://www.w3.org/TR/activitystreams-vocabulary/#dfn-orderedcollection">
<code>OrderedCollection</code></a>
specifically, while others are permitted to be either a
<a href="https://www.w3.org/TR/activitystreams-vocabulary/#dfn-collection">
<code>Collection</code></a>
or an
<a href="https://www.w3.org/TR/activitystreams-vocabulary/#dfn-orderedcollection">
<code>OrderedCollection</code></a>.
These
<a href="https://www.w3.org/TR/activitystreams-vocabulary/#dfn-orderedcollection">
<code>OrderedCollection</code></a>
objects MUST be presented consistently in reverse chronological order.
Collections defined in other vocabularies, including extensions,
are not subject to this requirement and can be unordered or ordered
by other criteria.
</p>
<p class="note">
What property is used to determine the reverse chronological order
is intentionally left as an implementation detail.
For example, many SQL-style databases use an incrementing integer
as an identifier, which can be reasonably used for handling
insertion order in most cases.
In other databases, an insertion time timestamp may be preferred.
What is used isn't important, but the ordering of elements must
remain intact, with newer items first.
A property which changes regularly, such a "last updated" timestamp,
should not be used.
</p>
<section id="outbox">
<h2>Outbox</h2>
<p>
The outbox is discovered through the <code>outbox</code>
property of an <a href="#actors">actor's</a> profile.
The <code>outbox</code> MUST be an
<a href="https://www.w3.org/TR/activitystreams-vocabulary/#dfn-orderedcollection">
<code>OrderedCollection</code></a>.
</p>
<p>
The outbox stream contains activities the user has
published, subject to the ability of the requestor to retrieve the
activity (that is, the contents of the outbox are filtered by the
permissions of the person reading it).
If a user submits a request without
<a href="#authorization">Authorization</a> the server should
respond with all of the <a href="#public-addressing">Public</a>
posts.
This could potentially be all relevant objects published by the
user, though the number of available items is left to the
discretion of those implementing and deploying the server.
</p>
<p>
The outbox accepts HTTP POST requests, with behaviour described in
<a href="#client-to-server-interactions">Client to Server
Interactions</a>.
</p>
</section>
<section id="inbox">
<h2>Inbox</h2>
<p>
The inbox is discovered through the <code>inbox</code>
property of an <a href="#actors">actor's</a> profile.
The <code>inbox</code> MUST be an