[docs] Tidy up federation docs into 'federating with gotosocial' section (#1392)

docs/federation/behaviors/request_throttling.md

@@ -1,3 +0,0 @@
-# Request Throttling and Rate Limiting
-
-GoToSocial applies rate limiting and http request throttling to the ActivityPub API endpoints (inboxes, user endpoints, emojis, etc). For more details on this, please see the [throttling](../../api/throttling.md) and [rate limiting](../../api/ratelimiting.md) documents.

docs/federation/federating_with_gotosocial/access_control.md

@@ -0,0 +1,11 @@
+# Access Control
+
+GoToSocial uses access control restrictions to protect users and resources from unwanted interactions with remote accounts and instances.
+
+As shown in the [http signatures](http_signatures.md) document, GoToSocial requires all incoming `GET` and `POST` requests from remote servers to be signed. Unsigned requests will be denied with http code `401 Unauthorized`.
+
+Access control restrictions are implemented by checking the `keyId` of the signature (who owns the public/private key pair making the request).
+
+First, the host value of the `keyId` uri is checked against the GoToSocial instance's list of blocked (defederated) domains. If the host is recognized as a blocked domain, then the http request will immediately be aborted with http code `403 Forbidden`.
+
+Next, GoToSocial will check for the existence of a block (in either direction) between the owner of the public key making the http request, and the owner of the resource that the request is targeting. If the GoToSocial user blocks the remote account making the request, then the request will be aborted with http code `403 Forbidden`.

docs/federation/federating_with_gotosocial/conversation_threads.md

@@ -6,8 +6,6 @@ With that said, it is possible to do 'best effort' dereferencing of threads, whe
 
 GoToSocial does this by iterating up and down the thread of a conversation, pulling in remote statuses where possible.
 
-## Example
-
 Let's say we have two accounts: `local_account` on `our.server`, and `remote_1` on `remote.1`.
 
 In this scenario, `local_account` follows `remote_1`, so posts from `remote_1` show up in the home timeline of `local_account`.
@@ -31,15 +29,3 @@ This process of thread dereferencing will likely involve making multiple HTTP ca
 The end result of this dereferencing is that, assuming the reblogged post by `remote_2` was part of a thread, then `local_account` should now be able to see posts in the thread when they open the status on their home timeline. In other words, they will see replies from accounts on other servers (who they may not have come across yet), in addition to any previous and next posts in the thread as posted by `remote_2`.
 
 This gives `local_account` a more complete view on the conversation, as opposed to just seeing the reblogged post in isolation and out of context. It also gives `local_account` the opportunity to discover new accounts to follow, based on replies to `remote_2`.
-
-## Privacy and Security
-
-During the dereferencing process, GoToSocial signs outgoing requests using the key of the actor who received the activity that necessitated dereferencing. To use the above example, this means that all dereferencing requests would be signed by `local_account`. This gives remote servers the ability to refuse these dereferencing requests, assuming that `local_account` is blocked by one or more participants in the conversation.
-
-From GoToSocial's side, domain blocks will be respected during the dereferencing process, to avoid making calls to servers that `our.server` has blocked.
-
-Individual account blocks will also be respected, meaning that `our.server` won't try to dereference posts from accounts blocked by `local_account`.
-
-Finally, GoToSocial expects that remote servers will only list replies that are marked as public (either `to` or `cc`). GtS may *try* to dereference followers-only posts, but it will assume that remote servers will check whether or not `local_account` is allowed to view them, and refuse accordingly.
-
-Of course, when `local_account` opens up the conversation thread in whatever application they are using, GoToSocial will apply the usual post visibility filtering to ensure that they do not see any posts that they shouldn't have access to.

docs/federation/federating_with_gotosocial/http_signatures.md

@@ -0,0 +1,69 @@
+# HTTP Signatures
+
+GoToSocial requires all `GET` and `POST` requests to ActivityPub s2s endpoints to be accompanied by a valid http signature.
+
+GoToSocial will also sign all outgoing `GET` and `POST` requests that it makes to other servers.
+
+This behavior is the equivalent of Mastodon's [AUTHORIZED_FETCH / "secure mode"](https://docs.joinmastodon.org/admin/config/#authorized_fetch).
+
+GoToSocial uses the [go-fed/httpsig](https://github.com/go-fed/httpsig) library for signing outgoing requests, and for parsing and validating the signatures of incoming requests. This library strictly follows the [Cavage http signature RFC](https://datatracker.ietf.org/doc/html/draft-cavage-http-signatures), which is the same RFC used by other implementations like Mastodon, Pixelfed, Akkoma/Pleroma, etc. (This RFC has since been superceded by the [httpbis http signature RFC](https://datatracker.ietf.org/doc/html/draft-ietf-httpbis-message-signatures), but this is not yet widely implemented.)
+
+## Incoming Requests
+
+GoToSocial request signature validation is implemented in [internal/federation](https://github.com/superseriousbusiness/gotosocial/blob/main/internal/federation/authenticate.go).
+
+GoToSocial will attempt to parse the signature using the following algorithms (in order), stopping at the first success:
+
+```text
+RSA_SHA256
+RSA_SHA512
+ED25519
+```
+
+## Outgoing Requests
+
+GoToSocial request signing is implemented in [internal/transport](https://github.com/superseriousbusiness/gotosocial/blob/main/internal/transport/signing.go).
+
+When assembling signatures:
+
+- outgoing `GET` requests use `(request-target) host date`
+- outgoing `POST` requests use `(request-target) host date digest` 
+
+GoToSocial uses the `RSA_SHA256` algorithm for signing requests, which is in line with other ActivityPub implementations.
+
+## Quirks
+
+The `keyId` used by GoToSocial in the `Signature` header will look something like the following:
+
+```text
+https://example.org/users/example_user/main-key
+```
+
+This is different from most other implementations, which usually use a fragment (`#`) in the `keyId` uri. For example, on Mastodon the user's key would instead be found at:
+
+```text
+https://example.org/users/example_user#main-key
+```
+
+For Mastodon, the public key of a user is served as part of that user's Actor representation. GoToSocial mimics this behavior when serving the public key of a user, but instead of returning the entire Actor at the `main-key` endpoint (which may contain sensitive fields), will return only a partial stub of the actor. This looks like the following:
+
+```json
+{
+  "@context": [
+    "https://w3id.org/security/v1",
+    "https://www.w3.org/ns/activitystreams"
+  ],
+  "id": "https://example.org/users/example_user",
+  "preferredUsername": "example_user",
+  "publicKey": {
+    "id": "https://example.org/users/example_user/main-key",
+    "owner": "https://example.org/users/example_user",
+    "publicKeyPem": "-----BEGIN PUBLIC KEY-----\nMIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEAzGB3yDvMl+8p+ViutVRG\nVDl9FO7ZURYXnwB3TedSfG13jyskoiMDNvsbLoUQM9ajZPB0zxJPZUlB/W3BWHRC\nNFQglE5DkB30GjTClNZoOrx64vLRT5wAEwIOjklKVNk9GJi1hFFxrgj931WtxyML\nBvo+TdEblBcoru6MKAov8IU4JjQj5KUmjnW12Rox8dj/rfGtdaH8uJ14vLgvlrAb\neQbN5Ghaxh9DGTo1337O9a9qOsir8YQqazl8ahzS2gvYleV+ou09RDhS75q9hdF2\nLI+1IvFEQ2ZO2tLk3umUP1ioa+5CWKsWD0GAXbQu9uunAV0VoExP4+/9WYOuP0ei\nKwIDAQAB\n-----END PUBLIC KEY-----\n"
+  },
+  "type": "Person"
+}
+```
+
+Remote servers federating with GoToSocial should extract the public key from the `publicKey` field. Then, they should use the `owner` field of the public key to further dereference the full version of the Actor, using a signed `GET` request.
+
+This behavior was introduced as a way of avoiding having remote servers make unsigned `GET` requests to the full Actor endpoint. However, this may change in future as it is not compliant and causes issues. Tracked in [this issue](https://github.com/superseriousbusiness/gotosocial/issues/1186).

docs/federation/federating_with_gotosocial/outbox.md

@@ -45,5 +45,3 @@ Note that the `OrderedCollection` itself contains no items. Callers must derefer
 The `orderedItems` array will contain up to 30 entries. To get more entries beyond that, the caller can use the `next` link provided in the response.
 
 Note that in the returned `orderedItems`, all activity types will be `Create`. On each activity, the `object` field will be the AP URI of an original public status created by the Actor who owns the Outbox (ie., a `Note` with `https://www.w3.org/ns/activitystreams#Public` in the `to` field, which is not a reply to another status). Callers can use the returned AP URIs to dereference the content of the notes.
-
-Contrary to the ActivityPub spec, GoToSocial will deny requests that are not HTTP signed--that is, unauthenticated requests. This is consistent with GoToSocial's authentication policies for other federation API endpoints. This is to ensure that GoToSocial can deny requests from domains or users that have been blocked either by the GoToSocial instance itself (domain block), or by the individual owner of the Outbox.

docs/federation/federating_with_gotosocial/request_throttling.md

@@ -0,0 +1,7 @@
+# Request Throttling and Rate Limiting
+
+GoToSocial applies http request throttling and rate limiting to the ActivityPub API endpoints (inboxes, user endpoints, emojis, etc).
+
+This ensures that remote servers cannot flood a GoToSocial instance with spurious requests. Instead, remote servers making GET or POST requests to the ActivityPub API endpoints should respect 429 and 503 http codes, and take account of the `retry-after` http response header.
+
+For more details on request throttling and rate limiting behavior, please see the [throttling](../../api/throttling.md) and [rate limiting](../../api/ratelimiting.md) documents.

docs/federation/security.md

@@ -1,7 +0,0 @@
-# Security
-
-TODO: describe the security model we use for federation.
-
-* http signatures
-* behavior for refusing requests
-* how data is protected

mkdocs.yml

@@ -56,10 +56,12 @@ nav:
   - "Federation":
     - "federation/index.md"
     - "federation/glossary.md"
-    - "federation/security.md"
-    - "federation/behaviors/outbox.md"
-    - "federation/behaviors/conversation_threads.md"
-    - "federation/behaviors/request_throttling.md"
+    - "Federating With GoToSocial":
+      - "federation/federating_with_gotosocial/http_signatures.md"
+      - "federation/federating_with_gotosocial/access_control.md"
+      - "federation/federating_with_gotosocial/request_throttling.md"
+      - "federation/federating_with_gotosocial/outbox.md"
+      - "federation/federating_with_gotosocial/conversation_threads.md"
   - "API Documentation":
     - "api/swagger.md"
     - "api/ratelimiting.md"