Conceptual overview of ActivityPub done

README.org

@@ -12,16 +12,106 @@
 # - ActivityPub is an actor model protocol.
 # - The general design can be understood from the overview section of the spec
 
+[[https://www.w3.org/TR/activitypub/][ActivityPub]] is a federated social network protocol.
+It is generally fairly easily understood by reading the
+[[https://en.wikipedia.org/wiki/Actor_model][Overview section of the standard]].
+In short, just as anyone can host their own email server, anyone can
+host their own ActivityPub server, and yet different users on different
+servers can interact.
+At the time of writing, ActivityPub is seeing major uptake, with
+several thousand nodes and several million registered users (with the
+caveat that registered users is not the same as active users).
+ActivityPub defines both a client-to-server and server-to-server
+protocol, but at this time the server-to-server protocol is what is
+most popular and is the primary concern of this article.
+
 # - In general, most of the design of ActivityPub is fairly clean, with
 #   a few exceptions
 
-#   - sharedInbox is a break from the actor model protocol and was a late
+ActivityPub's core design is fairly clean, following the
-#     addition
+[[https://en.wikipedia.org/wiki/Actor_model#Fundamental_concepts][actor model]].
+Different entities on the network can create other actors/objects
+(such as someone writing a note) and communicate via message passing.
+A core set of behaviors are defined in the spec for common message
+types, but the system is extensible so that implementations may define
+new terms with minimal ambiguity.
+If two instances both understand the same terms, they may be able to
+operate using behaviors not defined in the original protocol.
+This is called an "open world assumption" and is necessary for a
+protocol as general as ActivityPub; it would be extremely egotistical
+of the ActivityPub authors to assume that we could predict all future
+needs of users.[fn:json-ld]
+
+#   - (json-ld conversations outside of the scope of this particular post)
+
+Unfortunately (mostly due to time constraints and lack of consensus),
+even though most of what is defined in ActivityPub is fairly
+clean/simple, ActivityPub needed to be released with "holes in the
+spec".
+Certain key aspects critical to a functioning ActivityPub server are
+not specified:
+
 #   - authentication is not specified.  The community has settled
 #     on using http signatures for signing requests, though there is no
 #     "clean agreement" on how to attach signatures *to* posts yet.
 #   - authorization is not specified
-#   - (json-ld conversations outside of the scope of this particular post)
+
+ - Authentication is not specified.  Authentication is important to
+   verify "did this entity really say this thing".[fn:did-you-say-it]
+   However, the community has mostly converged on using [[https://tools.ietf.org/html/draft-cavage-http-signatures-11][HTTP Signatures]]
+   to sign requests when delivering posts to other users.
+   The advantage of HTTP Signatures is that they are extremely simple
+   to implement and require no normalization of message structure;
+   simply sign the body (and some headers) as-you-are-sending-it.
+   The disadvantage of HTTP Signatures is that this signature does
+   not "stick" to the original post and so cannot be "carried around"
+   the network.
+   A minority of implementations have implemented some early versions
+   of [[https://w3c-dvcg.github.io/ld-proofs/][Linked Data Proofs]] (formerly known as "Lined Data Signatures"),
+   however this requires access to a normalization algorithm that not
+   all users have a library for in their language, so Linked Data Proofs
+   have not as of yet caught on as popularly as HTTP Signatures.
+
+ - Authorization is also not specified.  (Authentication and
+   authorization are frequently confused (especially because in
+   English, the words are so similar) but mean two very different
+   things: the former is checking who said/did a thing, the latter is
+   checking whether they are allowed to do a thing.)  As of right now,
+   authorization tends to be extremely ad-hoc in ActivityPub systems,
+   sometimes as ad-hoc as unspecified heuristics from tracking who
+   received messages previously, who sent a message the first time,
+   and so on.  The primary way this is worked around is sadly that
+   interactions which require richer authorization simply have not
+   been rolled out onto the ActivityPub network.
+
+Compounding this situation is the general confusion/belief that
+autorization must stem from authentication.
+This document aims to show that not only is this not true, it is also
+a dangerous assumption with unintended consequences.
+An alternative approach based on "object capabilities" is
+demonstrated, showing that the actor model itself, if we take it at
+its purest form, is itself already a sufficient authorization system.
+
+#   - sharedInbox is a break from the actor model protocol and was a late
+#     addition
+
+Unfortunately there is a complication.
+At the last minute of ActivityPub's standardization, =sharedInbox= was
+added as a form of mutated behavior from the previously described
+=publicInbox= (which was a place for servers to share public content).
+The motivation of =sharedInbox= is admirable: while ActivityPub is based
+on explicit message sending to actors' =inbox= endpoints, if an actor
+on server A needs to send a message to 1000 followers on server B,
+why should server A make 1000 separate requests when it could do it
+in one?
+A good point, but the primary mistake in how this one request is made;
+rather than sending one message with a listing of all 1000 recipients
+on that server (which would preserve the actor model integrity),
+it was advocated that servers are already tracking follower information,
+so the receiving server can decide whom to send the message to.
+Unfortunately this decision breaks the actor model and also our suggested
+solution to authorization; see [[https://github.com/WebOfTrustInfo/rwot9-prague/blob/master/topics-and-advance-readings/ap-unwanted-messages.md#org7937fed][MultiBox]] for a suggestion on how we
+can solve this.
 
 # - What to do about the holes in the spec?  Many community members have
 #   asked that we codify current behavior.  However, as this document lays
@@ -34,14 +124,44 @@
 #   people who are actively concerned with human rights and the
 #   well-being of marginalized groups.
 
-** The mess we're in
+Despite these issues, ActivityPub has achieved major adoption.
+ActivityPub has the good fortune that its earliest adopters tended to
+be people who cared about human rights and the needs of marginalized
+groups, and spam has been relatively minimal.
 
+[fn:json-ld] The technology that ActivityPub uses to accomplish this is
+  called [[https://json-ld.org/][json-ld]] and admittedly has been one of the most controvercial
+  decisions in the ActivityPub specification.
+  Most of the objections have surrounded the unavailability of json-ld
+  libraries in some languages or the difficulty of mapping an open-world
+  assumption onto strongly typed systems without an "other data" bucket.
+  Since a project like ActivityPub must allow for the possibility of
+  extensions, we cannot escape open-world assumptions.
+  However, there may be things that can be done to improve happiness
+  about what extension mechanism is used; these discussions are out of
+  scope for this particular document, however.
 
+[fn:did-you-say-it] Or more accurately, since users may appoint
+  someone else to manage posting for them, "was this post really made
+  by someone who is authorized to speak on behalf of this entity".
 
+** Unwanted messages, from spam to harassment
+
+# - "there are no nazis on the fediverse"
+
+# - social networks: breadth vs depth?
+#   - wholesale borrowing of surveillance capitalist assumptions
+
+** Freedom of speech also means freedom to filter
 
 ** Don't pretend we can prevent what we can't
 
-** Freedom of speech also means freedom to filter
+# - introduce ocap community phrase
+# - introduce revised version
+
+# - "the fediverse is not indexed"
+
+# 
 
 ** Anti-solutions