Major cleanup

* Rename `fetch::keys` to `fetch::signatures`
* Clean up the public api of `fetch::signatures`
* Switch from axum to hyper
* Add request signature validation (buggy, wip)

Cargo.lock

@@ -89,78 +89,12 @@ dependencies = [
  "windows-sys 0.52.0",
 ]
 
-[[package]]
-name = "async-trait"
-version = "0.1.80"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "c6fa2087f2753a7da8cc1c0dbfcf89579dd57458e36769de5ac750b4671737ca"
-dependencies = [
- "proc-macro2",
- "quote",
- "syn 2.0.60",
-]
-
 [[package]]
 name = "autocfg"
 version = "1.2.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "f1fdabc7756949593fe60f30ec81974b613357de856987752631dea1e3394c80"
 
-[[package]]
-name = "axum"
-version = "0.7.5"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "3a6c9af12842a67734c9a2e355436e5d03b22383ed60cf13cd0c18fbfe3dcbcf"
-dependencies = [
- "async-trait",
- "axum-core",
- "bytes",
- "futures-util",
- "http",
- "http-body",
- "http-body-util",
- "hyper",
- "hyper-util",
- "itoa",
- "matchit",
- "memchr",
- "mime",
- "percent-encoding",
- "pin-project-lite",
- "rustversion",
- "serde",
- "serde_json",
- "serde_path_to_error",
- "serde_urlencoded",
- "sync_wrapper 1.0.1",
- "tokio",
- "tower",
- "tower-layer",
- "tower-service",
- "tracing",
-]
-
-[[package]]
-name = "axum-core"
-version = "0.4.3"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "a15c63fd72d41492dc4f497196f5da1fb04fb7529e631d73630d1b491e47a2e3"
-dependencies = [
- "async-trait",
- "bytes",
- "futures-util",
- "http",
- "http-body",
- "http-body-util",
- "mime",
- "pin-project-lite",
- "rustversion",
- "sync_wrapper 0.1.2",
- "tower-layer",
- "tower-service",
- "tracing",
-]
-
 [[package]]
 name = "backtrace"
 version = "0.3.71"
@@ -550,6 +484,8 @@ dependencies = [
  "chrono",
  "derive_more",
  "http",
+ "http-body-util",
+ "rand",
  "reqwest",
  "rsa",
  "serde_json",
@@ -987,12 +923,6 @@ dependencies = [
  "syn 2.0.60",
 ]
 
-[[package]]
-name = "matchit"
-version = "0.7.3"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "0e7465ac9959cc2b1404e8e2367b43684a6d13790fe23056cc8c6c5a6b7bcb94"
-
 [[package]]
 name = "memchr"
 version = "2.7.2"
@@ -1305,6 +1235,7 @@ dependencies = [
  "derive_more",
  "either",
  "fetch",
+ "serde_json",
  "store",
 ]
 
@@ -1415,7 +1346,7 @@ dependencies = [
  "serde",
  "serde_json",
  "serde_urlencoded",
- "sync_wrapper 0.1.2",
+ "sync_wrapper",
  "system-configuration",
  "tokio",
  "tokio-native-tls",
@@ -1507,12 +1438,6 @@ version = "1.4.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "ecd36cc4259e3e4514335c4a138c6b43171a8d61d8f5c9348f9fc7529416f247"
 
-[[package]]
-name = "rustversion"
-version = "1.0.15"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "80af6f9131f277a45a3fba6ce8e2258037bb0477a67e610d3c1fe046ab31de47"
-
 [[package]]
 name = "ryu"
 version = "1.0.17"
@@ -1594,16 +1519,6 @@ dependencies = [
  "serde",
 ]
 
-[[package]]
-name = "serde_path_to_error"
-version = "0.1.16"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "af99884400da37c88f5e9146b7f1fd0fbcae8f6eec4e9da38b67d05486f814a6"
-dependencies = [
- "itoa",
- "serde",
-]
-
 [[package]]
 name = "serde_urlencoded"
 version = "0.7.1"
@@ -1620,7 +1535,10 @@ dependencies = [
 name = "server"
 version = "0.0.0"
 dependencies = [
- "axum",
+ "http",
+ "http-body-util",
+ "hyper",
+ "hyper-util",
  "puppy",
  "serde_json",
  "tokio",
@@ -1770,12 +1688,6 @@ version = "0.1.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "2047c6ded9c721764247e62cd3b03c09ffc529b2ba5b10ec482ae507a4a70160"
 
-[[package]]
-name = "sync_wrapper"
-version = "1.0.1"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "a7065abeca94b6a8a577f9bd45aa0867a2238b74e8eb67cf10d492bc39351394"
-
 [[package]]
 name = "system-configuration"
 version = "0.5.1"

bin/server/Cargo.toml

@@ -4,6 +4,9 @@ edition = "2021"
 
 [dependencies]
 puppy = { path = "../../lib/puppy" }
+hyper = { version = "*", features = ["full"] }
 tokio = { version = "*", features = ["full"] }
-axum = "*"
+http-body-util = "*"
+hyper-util = { version = "*", features = ["full"] }
 serde_json = "*"
+http = "*"

bin/server/src/api.rs

@@ -0,0 +1,140 @@
+//! API endpoints and request handlers.
+
+pub mod ap {
+    //! ActivityPub handlers.
+
+    use http_body_util::Full;
+    use hyper::body::Bytes;
+    use puppy::{
+        actor::Actor,
+        auth::{Signer, Verifier},
+        config::Config,
+        data::{Id, PrivateKey, PublicKey},
+        fetch::{signatures::Private, SigningKey},
+        get_local_ap_object, Key,
+    };
+    use serde_json::{to_string, Value};
+    use crate::{respond, Response};
+
+    /// Proxy a request through the instance.
+    pub async fn proxy(params: &[(&str, &str)]) -> Response {
+        // Extract our query parameters.
+        let Some(user) = params.iter().find_map(|(k, v)| (*k == "user").then_some(v)) else {
+            return respond(400, Some("Expected `user` query param"), []);
+        };
+        let Some(url) = params.iter().find_map(|(k, v)| (*k == "url").then_some(v)) else {
+            return respond(400, Some("Expected `url` query param"), []);
+        };
+
+        // Look up the actor's key in the store (which is accessible through the puppy context).
+        let (signing_key) = puppy::context::<_, puppy::Error>(|cx| try {
+            let actor = Actor::by_username(&cx, user)?.unwrap();
+            let (PrivateKey { key_pem, .. }, PublicKey { key_id, .. }) =
+                cx.store().get_mixin_many(actor.key)?;
+            let Id(owner) = cx.store().get_alias(actor.key)?.unwrap();
+            let inner = Private::decode_pem(&key_pem);
+            SigningKey { key_id, owner, inner }
+        })
+        .unwrap();
+
+        eprintln!("proxy: params: {params:?}");
+        // Proxy the request through our fetcher.
+        let resp = puppy::fetch::forward(&signing_key, url).await.unwrap();
+        eprintln!("proxy: status = {}", resp.status());
+
+        // Convert the http-types request to a hyper request.
+        resp.map(Bytes::from).map(Full::new).into()
+    }
+
+    /// Handle POSTs to actor inboxes. Requires request signature.
+    pub fn inbox(actor_id: &str, sig: Signer, body: Value, cfg: Config) -> Response {
+        todo!()
+    }
+
+    /// Serve an ActivityPub object as json-ld.
+    pub fn serve_object(object_ulid: &str) -> Response {
+        let Ok(parsed) = object_ulid.parse::<Key>() else {
+            return respond(400, Some("improperly formatted id"), []);
+        };
+        let result = puppy::context(|cx| get_local_ap_object(&cx, parsed));
+        let Ok(object) = result else {
+            return respond(404, <Option<String>>::None, []);
+        };
+        let json = to_string(&object.to_json_ld()).unwrap();
+        respond(200, Some(json), [AP_CONTENT_TYPE])
+    }
+
+    const AP_CONTENT_TYPE: (&str, &str) = ("content-type", "application/activity+json");
+
+    /// Serve the special actor used for signing requests.
+    pub fn serve_verifier_actor(cfg: Config) -> Response {
+        let body = Verifier::load(&cfg).to_json_ld();
+        let encoded = serde_json::to_vec(&body).unwrap();
+        respond(200, Some(encoded), [AP_CONTENT_TYPE])
+    }
+}
+
+pub mod wf {
+    //! WebFinger endpoints and related stuff.
+
+    use puppy::{config::Config, data::Username, Error};
+    use serde_json::json;
+
+    use crate::{respond, Response};
+
+    const WF_CONTENT_TYPE: (&str, &str) = ("content-type", "application/jrd+json");
+
+    pub fn resolve(query: &[(&str, &str)], cfg: Config) -> Response {
+        match query.iter().find_map(get_handle) {
+            // Serve JRDs for local actors.
+            Some(handle) if cfg.wf_domain == handle.instance => {
+                let id = puppy::context::<_, Error>(|cx| try {
+                    let user = cx
+                        .store()
+                        .lookup(Username(handle.username.to_string()))?
+                        .unwrap();
+                    let id = cx.store().get_alias::<puppy::data::Id>(user)?.unwrap().0;
+                    id
+                })
+                .unwrap();
+                let jrd = json!({
+                  "subject": format!("acct:{}@{}", handle.username, handle.instance),
+                  "links": [
+                    {
+                      "rel": "self",
+                      "type": "application/activity+json",
+                      "href": id
+                    },
+                  ]
+                });
+                let encoded = serde_json::to_vec(&jrd).unwrap();
+                respond(200, Some(encoded), [WF_CONTENT_TYPE])
+            }
+            Some(_) => todo!(),
+            None => todo!("bad request: could not find valid resource parameter"),
+        }
+    }
+
+    pub struct Handle<'x> {
+        username: &'x str,
+        instance: &'x str,
+    }
+
+    /// Parse the `resource` parameter into a [`Handle`].
+    pub fn get_handle<'x>((k, v): &'x (&str, &str)) -> Option<Handle<'x>> {
+        // We're looking for the `resource` query parameter.
+        if *k == "resource" {
+            // This prefix needs to exist according to spec.
+            v.strip_prefix("acct:")?
+                // Some implementations may prefix with `@`. its ok if it's there and its also ok
+                // if its not there, so we use `trim_start_matches` instead of `strip_prefix`.
+                .trim_start_matches('@')
+                // Split on the middle `@` symbol, which separates the username and instance bits
+                .split_once('@')
+                // Convert to a structured format.
+                .map(|(username, instance)| Handle { username, instance })
+        } else {
+            None
+        }
+    }
+}

bin/server/src/main.rs

@@ -1,79 +1,237 @@
-#![feature(try_blocks)]
+#![feature(try_blocks, yeet_expr)]
-use std::collections::HashMap;
 
-use axum::{
+use std::convert::Infallible;
-    extract::{Path, Query},
+use std::net::SocketAddr;
-    response::{AppendHeaders, IntoResponse as _},
+
-    routing::get,
+use http::request::Parts;
-    Json, Router,
+use http_body_util::{BodyExt as _, Full};
-};
+use hyper::body::Bytes;
-use puppy::{
+use hyper::server::conn::http1;
-    actor::Actor,
+use hyper::service::service_fn;
-    context,
+use hyper_util::rt::TokioIo;
-    data::{PrivateKey, PublicKey},
+use puppy::auth::{SigError, Signer};
-    get_local_ap_object, Key,
+use puppy::{auth::verify_signature, config::Config};
-};
+use puppy::fetch::signatures::Signature;
-use serde_json::json;
+use serde_json::{from_slice, json, Value};
+use tokio::net::TcpListener;
 
 #[tokio::main]
 async fn main() {
-    let app = Router::new()
+    let config = Config {
-        .route(
+        ap_domain: "test.piss-on.me".to_string(),
-            "/o/:ulid",
+        wf_domain: "test.piss-on.me".to_string(),
-            get(
+        port: 1312,
-                |Path(raw_object_id): Path<String>, req: axum::extract::Request| async move {
+    };
-                    eprintln!("req: {req:?}");
+    start(&config).await.unwrap();
-                    context::<_, puppy::Error>(|cx| try {
+}
-                        let object_id = raw_object_id.parse::<Key>().unwrap();
+
-                        let obj = get_local_ap_object(&cx, object_id).unwrap().to_json_ld();
+pub async fn start(cfg: &Config) -> Result<(), Box<dyn std::error::Error + Send + Sync>> {
-                        (
+    let addr = SocketAddr::from(([127, 0, 0, 1], cfg.port));
-                            AppendHeaders([("content-type", "application/activity+json")]),
+    let listener = TcpListener::bind(addr).await?;
-                            Json(obj).into_response(),
+
-                        )
+    // We start a loop to continuously accept incoming connections
-                    })
+    loop {
-                    .unwrap()
+        let (stream, _) = listener.accept().await?;
-                },
+
-            ),
+        // Use an adapter to access something implementing `tokio::io` traits as if they implement
-        )
+        // `hyper::rt` IO traits.
-        .route(
+        let io = TokioIo::new(stream);
-            "/proxy",
+
-            get(|Query(q): Query<HashMap<String, String>>| async move {
+        let cfg = cfg.clone();
-                let (key_pem, key_id) = context::<_, puppy::Error>(|cx| try {
+        // Spawn a tokio task to serve multiple connections concurrently
-                    let actor = Actor::by_username(&cx, "riley")?.unwrap();
+        tokio::task::spawn(async move {
-                    let (private, public) = cx
+            // Finally, we bind the incoming connection to our `hello` service
-                        .store()
+            if let Err(err) = http1::Builder::new()
-                        .get_mixin_many::<(PrivateKey, PublicKey)>(actor.key)?;
+                // `service_fn` converts our function in a `Service`
-                    (private.key_pem, public.key_id)
+                .serve_connection(io, service_fn(|req| handle(req, cfg.clone())))
-                })
+                .await
-                .unwrap();
+            {
-                puppy::fetch::resolve(&key_pem, &key_id, &q["target"])
+                eprintln!("Error serving connection: {:?}", err);
-                    .await
+            }
-                    .unwrap()
+        });
-            }),
+    }
-        )
+}
-        .route(
+
-            "/.well-known/webfinger",
+type Request = hyper::Request<hyper::body::Incoming>;
-            get(
+type Response<T = Full<Bytes>> = hyper::Response<T>;
-                |Query(q): Query<HashMap<String, String>>, req: axum::extract::Request| async move {
+
-                    eprintln!("req: {req:?}");
+/// The request handler.
-                    let Some(rest) = q["resource"].strip_prefix("acct:") else {
+async fn handle(req: Request, cfg: Config) -> Result<Response, Infallible> {
-                        panic!("{q:?}");
+    // We need to fetch the entire body of the request for signature validation, because that involves making
-                    };
+    // a digest of the request body in some cases.
-                    if rest == "riley@test.piss-on.me" {
+    let request = {
-                        Json(json!({
+        let (req, body) = req.into_parts();
-                            "subject": "acct:riley@test.piss-on.me",
+        let Ok(body) = body.collect().await.map(|b| b.to_bytes()) else {
-                            "links": [{
+            return Ok(error::invalid_body("Could not get request body"));
-                                "rel": "self",
+        };
-                                "type": "application/activity+json",
+        http::Request::from_parts(req, body)
-                                "href": "https://test.piss-on.me/o/01HWG4BQJR23TWF12KVPBBP1HG",
+    };
-                            }],
+    // Simplified representation of a request, so we can pattern match on it more easily in the dispatchers.
-                        }))
+    let req = make_req(&request);
-                    } else {
+    eprintln!("{request:?}: open");
-                        panic!("{rest:?}")
+    // We'll use the path to pick where specifically to send the request.
-                    }
+    // Check request signature at the door. Even if it isn't needed for a particular endpoint, failing fast
-                },
+    // with a clear error message will save anyone trying to get *their* signatures implementation a major
-            ),
+    // headache.
-        );
+    let res = match verify_signature(&request, &cfg).await {
-    let sock = tokio::net::TcpListener::bind("0.0.0.0:1312").await.unwrap();
+        // If the request was signed and the signature was accepted, they can access the protected endpoints.
-    axum::serve(sock, app).await.unwrap();
+        Ok(Some(sig)) => dispatch_signed(req, sig, cfg).await,
+        // Unsigned requests can see a smaller subset of endpoints, most notably the verification actor.
+        Ok(None) => dispatch_public(req, cfg).await,
+        // If a signature was provided *but it turned out to be unverifiable*, show them the error message.
+        Err(err) => error::bad_signature(match err {
+            SigError::VerificationFailed { error } => format!("Verification failed: {error}"),
+            SigError::ParseSignature { error } => format!("Failed to parse signature: {error}"),
+            SigError::FailedToFetchKey { keyid } => format!("Failed to fetch {keyid}"),
+        }),
+    };
+    eprintln!(
+        "{} {}: done (status: {})",
+        request.method(),
+        request.uri(),
+        res.status()
+    );
+    Ok(res)
+}
+
+// A parsed HTTP request for easy handling.
+struct Req<'a> {
+    method: &'a Method,
+    body: Bytes,
+    // URI bits
+    params: Vec<(&'a str, &'a str)>,
+    path: Vec<&'a str>,
+}
+
+impl Req<'_> {
+    fn path(&self) -> &[&str] {
+        &self.path
+    }
+}
+
+fn make_req<'x>(r: &'x http::Request<Bytes>) -> Req<'x> {
+    let path: Vec<&str> = r
+        .uri()
+        .path()
+        .split('/')
+        .filter(|s| !s.is_empty())
+        .collect();
+    let params: Vec<(&str, &str)> = r
+        .uri()
+        .query()
+        .into_iter()
+        .flat_map(|s| s.split('&'))
+        .filter_map(|s| s.split_once('='))
+        .collect();
+    Req {
+        method: r.method(),
+        body: r.body().clone(),
+        params,
+        path,
+    }
+}
+
+use hyper::Method;
+
+const POST: &Method = &Method::POST;
+const GET: &Method = &Method::GET;
+
+/// Handle a signed and verified request.
+///
+/// This function is where all requests to a protected endpoint have to go through. If the request
+/// was signed but does not target a protected endpoint, this function will fall back to the
+/// [`dispatch_public`] handler.
+async fn dispatch_signed(req: Req<'_>, sig: Signer, cfg: Config) -> Response {
+    eprintln!("Dispatching signed request");
+    match (req.method, req.path()) {
+        // Viewing ActivityPub objects requires a signed request, i.e. "authorized fetch".
+        // The one exception for this is `/s/request-verifier`, which is where the request
+        // verification actor lives.
+        (GET, ["o", ulid]) => api::ap::serve_object(ulid),
+        // POSTs to an actor's inbox need to be signed to prevent impersonation.
+        (POST, ["o", ulid, "inbox"]) => with_json(&req.body, |json| {
+            // We only handle the intermediate parsing of the json, full resolution of the
+            // activity object will happen inside the inbox handler itself.
+            api::ap::inbox(ulid, sig, json, cfg)
+        }),
+        // Try the resources for which no signature is required as well.
+        _ => dispatch_public(req, cfg).await,
+    }
+}
+
+/// Dispatch `req` to an unprotected endpoint. If the requested path does not exist, the
+/// function will return a 404 response.
+async fn dispatch_public(req: Req<'_>, cfg: Config) -> Response {
+    eprintln!("Dispatching public request");
+    match (req.method, req.path()) {
+        (GET, ["proxy"]) => api::ap::proxy(&req.params).await,
+        (GET, [".well-known", "webfinger"]) => api::wf::resolve(&req.params, cfg),
+        (GET, ["s", "request-verifier"]) => api::ap::serve_verifier_actor(cfg),
+        (m, p) => {
+            eprintln!("404: {m} {p:?}");
+            error::not_found()
+        }
+    }
+}
+
+fn with_json(body: &[u8], f: impl FnOnce(Value) -> Response) -> Response {
+    let Ok(json) = from_slice(body) else {
+        return error::invalid_body("Could not decode as JSON");
+    };
+    f(json)
+}
+
+/// A quick, simple way to construct a response.
+fn respond<const N: usize>(
+    status: u16,
+    body: Option<impl Into<Bytes>>,
+    headers: [(&str, &str); N],
+) -> Response {
+    let mut resp = Response::<()>::builder().status(status);
+    for (name, data) in headers {
+        resp = resp.header(name, data);
+    }
+    resp.body(match body {
+        Some(bytes) => Full::new(bytes.into()),
+        None => Full::new(Bytes::default()),
+    })
+    .unwrap()
+}
+
+mod api;
+
+mod error {
+    //! Pre-baked error responses.
+
+    use http_body_util::Full;
+    use super::Response;
+
+    /// 404 response.
+    pub fn not_found() -> Response {
+        let body = Full::new("Not found".into());
+        Response::<()>::builder()
+            .status(404)
+            .header("content-type", "text/plain")
+            .body(body)
+            .unwrap()
+    }
+
+    /// 403 response indicating a bad request signature.
+    pub fn bad_signature(err: String) -> Response {
+        let body = Full::new(err.into());
+        Response::<()>::builder()
+            .status(403)
+            .header("content-type", "text/plain")
+            .body(body)
+            .unwrap()
+    }
+
+    pub fn invalid_body(err: impl ToString) -> Response {
+        let body = Full::new(err.to_string().into());
+        Response::<()>::builder()
+            .status(400)
+            .header("content-type", "text/plain")
+            .body(body)
+            .unwrap()
+    }
 }

lib/fetch/Cargo.toml

@@ -6,11 +6,13 @@ edition = "2021"
 path = "src/lib.rs"
 
 [dependencies]
-reqwest     = "*"
+reqwest        = { version = "*", features = ["json"] }
-sigh        = "*"
+sigh           = "*"
-serde_json  = "*"
+serde_json     = "*"
-derive_more = "*"
+derive_more    = "*"
-http        = "*"
+http           = "*"
-chrono      = "*"
+chrono         = "*"
-base64      = "*"
+base64         = "*"
-rsa         = { version = "*", features = ["sha2"] }
+rsa            = { version = "*", features = ["sha2"] }
+http-body-util = "*"
+rand           = "*"

lib/fetch/src/lib.rs

@@ -1,14 +1,14 @@
-#![feature(iter_intersperse)]
+#![feature(iter_intersperse, yeet_expr)]
 use chrono::Utc;
 use derive_more::{Display, From, Into};
+use http_body_util::BodyExt as _;
+use signatures::{Private, Public};
 use reqwest::Body;
 use serde_json::{json, Value};
-use sigh::{
-    alg::{Hs2019, RsaSha256},
-    Key as _, SigningConfig,
-};
 
-use crate::keys::{HS2019, RSA_SHA256};
+use crate::signatures::HS2019;
+
+pub use http;
 
 pub enum Object {
     Activity(Activity),
@@ -69,44 +69,66 @@ where
 }
 
 /// Deliver an [`Activity`] to a particular `inbox`.
-pub async fn deliver(private_key_pem: &str, key_id: &str, activity: Activity, inbox: &str) -> () {
+pub async fn deliver(key: &SigningKey, activity: Activity, inbox: &str) -> () {
-    let body = serde_json::to_string_pretty(&activity.to_json_ld()).unwrap();
+    todo!()
-    let mut req = http::Request::post(inbox)
-        .header("content-type", "application/activity+json")
-        .header("user-agent", "ActivityPuppy/0.0.0 (delivery)")
-        .header("date", Utc::now().to_rfc3339())
-        .body(body)
-        .unwrap();
-    let key = sigh::PrivateKey::from_pem(private_key_pem.as_bytes()).unwrap();
-    SigningConfig::new(RsaSha256, &key, key_id)
-        .sign(&mut req)
-        .unwrap();
-    reqwest::Client::new()
-        .execute(req.try_into().unwrap())
-        .await
-        .unwrap();
 }
 
-pub async fn resolve(private_key_pem: &str, key_id: &str, target: &str) -> reqwest::Result<String> {
+pub async fn resolve(key: &SigningKey, target: &str) -> reqwest::Result<Value> {
-    const EMPTY_DIGEST: &str = "sha-256=47DEQpj8HBSa+/TImW+5JCeuQeRkm5NMpJWZG3hSuFU=";
+    // TODO: make this retry with different signature options and remember what works for the
+    // particular host.
+
+    // Sun, 06 Nov 1994 08:49:37 GMT
+    const RFC_822: &str = "%a, %d %b %Y %H:%M:%S GMT";
+
+    let date = Utc::now().format(RFC_822).to_string();
+    let mut req = http::Request::builder()
+        .uri(target)
+        .header("accept", "application/activity+json")
+        .header("user-agent", "ActivityPuppy/0.0.0 (resolver)")
+        .header("date", date)
+        // Empty body
+        .body(())
+        .unwrap();
+
+    // hs2019 works with masto
+    key.sign(HS2019, &req)
+        .expect("signing error")
+        .attach_to(&mut req);
+
+    reqwest::Client::new()
+        .execute(req.map(|_| Body::default()).try_into().unwrap())
+        .await?
+        .json()
+        .await
+}
+
+pub async fn forward(key: &SigningKey, target: &str) -> reqwest::Result<http::Response<String>> {
     // Sun, 06 Nov 1994 08:49:37 GMT
     const RFC_822: &str = "%a, %d %b %Y %H:%M:%S GMT";
 
     let date = Utc::now().format(RFC_822).to_string();
     let mut req = http::Request::get(target)
-        .header("accept", "application/json")
+        .header("accept", "application/activity+json")
         .header("user-agent", "ActivityPuppy/0.0.0 (resolver)")
         .header("date", date)
         // Empty body
-        .body(Body::default())
+        .body(())
         .unwrap();
     // hs2019 works with masto
-    keys::sign(&mut req, HS2019, private_key_pem, key_id).unwrap();
+    key.sign(HS2019, &req)
-    reqwest::Client::new()
+        .expect("signing error")
-        .execute(req.try_into().unwrap())
+        .attach_to(&mut req);
-        .await?
+
-        .text()
+    let resp = reqwest::Client::new()
-        .await
+        .execute(req.map(|_| Body::default()).try_into().unwrap())
+        .await?;
+
+    let http_resp: http::Response<reqwest::Body> = resp.into();
+    let (res, body) = http_resp.into_parts();
+    let body = body.collect().await.unwrap().to_bytes();
+    let http_resp =
+        http::Response::from_parts(res, String::from_utf8_lossy(body.as_ref()).into_owned());
+    Ok(http_resp)
 }
 
 /// An actor is an entity capable of producing Takes.
@@ -121,7 +143,7 @@ pub struct Actor {
     pub display_name: Option<String>,
     /// Public counterpart to the signing key used to sign activities
     /// generated by the actor.
-    pub public_key: PublicKey,
+    pub public_key: Key,
 }
 
 impl Actor {
@@ -138,97 +160,280 @@ impl Actor {
             "name": self.display_name,
             "type": "Person",
             "publicKey": {
-                "id": self.public_key.key_id.to_string(),
+                "id": self.public_key.key_id,
-                "publicKeyPem": self.public_key.public_key_pem,
+                "publicKeyPem": self.public_key.inner,
                 "owner": self.id.to_string(),
             }
         })
     }
 }
 
-pub struct PublicKey {
+/// A key that can be used to verify a request signature.
-    pub key_id: Id,
+pub type VerificationKey = Key<Public>;
-    pub owner: Id,
+
-    pub public_key_pem: String,
+/// A key that can be used to sign a request.
+pub type SigningKey = Key<Private>;
+
+/// A key used for authorized fetch.
+///
+/// It comes in several flavors:
+///
+/// - `Key` (`K` = [`String`]): PEM-encoded, can be turned into a JSON object.
+/// - [`VerificationKey`] (`K` = [`Public`]): used as an input in the request signature validation process.
+/// - [`SigningKey`] (`K` = [`Private`]): used as an input in the generation of a signed request.
+pub struct Key<K = String> {
+    /// The `"id"` property of the public key.
+    pub key_id: String,
+    /// The `"owner"` property.
+    pub owner: String,
+    /// Maps to the `"publicKeyPem"` property of an actor's `"publicKey"` when (de)serializing, and when the
+    /// key is used for doing [signatures].
+    pub inner: K,
+}
+
+impl Key {
+    /// Tries to find the PEM-encoded public key from the result of fetching a key id.
+    pub fn from_json(json: Value) -> Option<Key> {
+        // First, we try the object itself.
+        json.as_object().and_then(Key::from_map).or_else(|| {
+            // Because of how mastodon deals with pubkey resolution, most implementations will serve the whole actor
+            // object instead of just the key, so we try that first, because it is the de facto standard.
+            json["publicKey"].as_object().and_then(Key::from_map)
+        })
+    }
+    /// Construct
+    fn from_map(map: &serde_json::Map<String, Value>) -> Option<Key> {
+        Some(Key {
+            key_id: map["id"].as_str().map(str::to_owned)?,
+            owner: map["owner"].as_str().map(str::to_owned)?,
+            inner: map["publicKeyPem"].as_str().map(str::to_owned)?,
+        })
+    }
+    /// "Upgrade" a pem-encoded public key to a key that can actually be used for requests.
+    pub fn upgrade(self) -> Key<Public> {
+        let inner = Public::decode_pem(&self.inner);
+        Key {
+            key_id: self.key_id,
+            owner: self.owner,
+            inner,
+        }
+    }
+}
+
+impl Key<Public> {
+    /// Encode a verification key so that it can be presented in a json.
+    pub fn serialize(self) -> Key {
+        let public_key_pem = self.inner.encode_pem();
+        Key {
+            key_id: self.key_id,
+            owner: self.owner,
+            inner: public_key_pem,
+        }
+    }
 }
 
 #[derive(Display, From, Into, Debug, Clone)]
 pub struct Id(String);
 
-pub mod keys {
+pub mod signatures {
-    //! Cryptography and such.
+    //! Containment zone for the funny math that doesn't make much sense to puppy.
+    //!
+    //! This module provides ActivityPuppy's HTTP signatures implementation. The state of HTTP signatures implementations
+    //! is, to put it mildly, *een fucking kutzooi*. For historical reasons, no one implements it *exactly* right (much
+    //! like URI parsers). This implementation aims to be as broadly compatible as possible.
+    //!
+    //! The only non-deprecated [`Algorithm`] is [`"hs2019"`][HS2019], but not everyone implements it, because the initial
+    //! round of implementations of the spec were based on a draft, and [`"rsa-sha256"`][RSA_SHA256] is kinda the de facto
+    //! standard.
+    //!
+    //! # Behavior
+    //!
+    //! By default, puppy will sign with `algorithm="hs2019"` (using `(created)` and `(expires)` pseudo-headers), and retry
+    //! in legacy mode (using `algorithm="rsa-sha256"` with `date` header) if the signature gets rejected.
+    //!
+    //! Currently, `"hs2019"` is treated as equivalent to `"rsa-sha256"` for verification purposes. Support for elliptic
+    //! curve keys is planned, but not a priority.
+    //!
+    //! # Links
+    //!
+    //! More information about http signatures:
+    //!
+    //! - <https://swicg.github.io/activitypub-http-signature>
+    //! - <https://datatracker.ietf.org/doc/html/draft-cavage-http-signatures>
 
-    use chrono::{TimeDelta, Utc};
+    use std::{borrow::Cow, collections::HashMap, path::Path};
+
+    use chrono::{DateTime, TimeDelta, Utc};
     use http::{HeaderValue, Method, Request};
-    use reqwest::Body;
+    use rsa::{
-    use rsa::{pkcs1v15::SigningKey, pkcs8::DecodePrivateKey as _, sha2};
+        signature::{Verifier as _, Signer as _, SignatureEncoding as _},
-    use sigh::{
+        pkcs1v15::{SigningKey, VerifyingKey},
-        Key as _,
+        pkcs8::{
-        alg::{Algorithm as _, RsaSha256},
+            DecodePrivateKey, DecodePublicKey, EncodePublicKey as _, EncodePrivateKey as _,
+            LineEnding,
+        },
+        sha2::{self, Sha256},
+        RsaPrivateKey,
     };
 
-    pub struct RawPrivateKey {
+    use base64::prelude::*;
-        inner: sigh::PrivateKey,
-    }
 
-    impl RawPrivateKey {
+    /// A key that can be used to generate signatures.
-        pub fn to_pem(&self) -> String {
+    #[derive(Clone)]
-            self.inner.to_pem().unwrap()
+    pub struct Private(rsa::RsaPrivateKey);
+
+    impl Private {
+        /// Generate a new keypair.
+        pub fn gen() -> (Private, Public) {
+            let mut rng = rand::thread_rng();
+            let bits = 4096;
+            let private = RsaPrivateKey::new(&mut rng, bits).unwrap();
+            let public = private.to_public_key();
+            (Private(private), Public(public))
+        }
+        /// Get the public counterpart to this key.
+        pub fn get_public(&self) -> Public {
+            Public(self.0.to_public_key())
+        }
+        /// Load a private key from a file on disk.
+        pub fn load(path: impl AsRef<Path>) -> Private {
+            use rsa::pkcs8::DecodePrivateKey;
+            DecodePrivateKey::read_pkcs8_pem_file(path)
+                .map(Private)
+                .unwrap()
+        }
+        /// PEM-encode the key PKCS#8 style.
+        pub fn encode_pem(&self) -> String {
+            self.0
+                .to_pkcs8_pem(LineEnding::default())
+                .unwrap()
+                .to_string()
+        }
+        /// Decode the key from a PKCS#8 PEM-encoded string.
+        pub fn decode_pem(pkcs8_pem: &str) -> Private {
+            DecodePrivateKey::from_pkcs8_pem(&pkcs8_pem)
+                .map(Private)
+                .unwrap()
         }
     }
 
-    pub struct RawPublicKey {
+    /// A key that can be used to verify signatures.
-        inner: sigh::PublicKey,
+    #[derive(Clone)]
-    }
+    pub struct Public(rsa::RsaPublicKey);
 
-    impl RawPublicKey {
+    impl Public {
-        pub fn to_pem(&self) -> String {
+        /// PEM-encode the public key in accordance with PKCS#8.
-            self.inner.to_pem().unwrap()
+        pub fn encode_pem(&self) -> String {
+            self.0
+                .to_public_key_pem(LineEnding::default())
+                .unwrap()
+                .to_string()
+        }
+        /// Decode a PKCS#8 PEM-encoded public key from a string.
+        pub fn decode_pem(pkcs8_pem: &str) -> Public {
+            DecodePublicKey::from_public_key_pem(&pkcs8_pem)
+                .map(Public)
+                .unwrap()
         }
     }
 
-    /// Generate a private and public keypair.
+    impl crate::SigningKey {
-    pub fn gen_keypair() -> (RawPrivateKey, RawPublicKey) {
+        /// Create a signature for `req` using the given algorithm, for `GET` requests.
-        let (private, public) = RsaSha256.generate_keys().unwrap();
+        pub fn sign(&self, alg: Algorithm, req: &Request<()>) -> Result<Signature<'_>, String> {
-        (RawPrivateKey { inner: private }, RawPublicKey {
+            let pieces = gather_pieces(&req)?;
-            inner: public,
+            let signing_string = make_signing_string(&pieces);
-        })
+            let signature = create(signing_string, alg, &self.inner, &self.key_id, pieces)?;
+            Ok(signature)
+        }
+        /// Create a signature for `req` using the given algorithm, and calculate and attach the `digest` header to
+        /// the request (if it doesn't already have one).
+        ///
+        /// This is required by most implementations when POSTing to an inbox.
+        pub fn sign_with_digest<T>(
+            &self,
+            alg: Algorithm,
+            req: &mut Request<T>,
+        ) -> Result<Signature<'_>, String>
+        where
+            T: AsRef<[u8]>,
+        {
+            todo!()
+        }
+    }
+
+    impl crate::VerificationKey {
+        /// Verify the request's signature.
+        pub fn verify(&self, sig: Signature<'_>) -> Result<(), String> {
+            use rsa::pkcs1v15::Signature;
+            // TODO: support elliptic curve keys
+            // TODO: nicer error reporting
+            let Public(key) = self.inner.clone();
+            let verifying_key = VerifyingKey::<Sha256>::new(key);
+            let decoded = BASE64_STANDARD
+                .decode(&sig.signature_encoded)
+                .map_err(|e| e.to_string())?;
+            let signature = Signature::try_from(decoded.as_slice()).map_err(|e| e.to_string())?;
+            verifying_key
+                .verify(sig.signing_string.as_bytes(), &signature)
+                .map_err(|e| e.to_string())
+        }
     }
 
     /// The algorithm to sign with.
-    #[derive(PartialEq, Debug)]
+    ///
+    /// Your two options are:
+    ///
+    /// - [`hs2019`][HS2019], the *correct* option
+    /// - [`"rsa-sha256"`][RSA_SHA256], the most compatible option
+    #[derive(PartialEq, Debug, Clone, Copy)]
     pub struct Algorithm(&'static str);
 
-    pub const RSA_SHA256: Algorithm = Algorithm("rsa-sha256");
+    /// `hs2019`, the only non-deprecated HTTP signatures algorithm.
     pub const HS2019: Algorithm = Algorithm("hs2019");
+    /// The HTTP signatures algorithm everyone uses, `rsa-sha256`.
+    pub const RSA_SHA256: Algorithm = Algorithm("rsa-sha256");
 
-    struct Signature<'k> {
+    /// A signature derived from an [`http::Request`].
+    pub struct Signature<'k> {
         key_id: &'k str,
         alg: Algorithm,
         components: Vec<Component>,
         created: String,
         expires: String,
-        /// Base64-encoded signature.
+        signing_string: Cow<'k, str>,
         signature_encoded: String,
     }
 
-    /// Sign `req`.
+    impl Signature<'_> {
-    pub fn sign(
+        /// Obtain the key id for the signature.
-        req: &mut Request<Body>,
+        pub fn key_id(&self) -> &str {
-        alg: Algorithm,
+            &self.key_id
-        private_key: &str,
+        }
-        key_id: &str,
+        /// Get the time the signature was created. This information is extracted from the `(created)`
-    ) -> Result<(), String> {
+        /// pseudo-header if it is defined, and the `date` http header otherwise.
-        // NOTE: Rough translation of https://nest.pijul.org/ez/ActivityPuppy:main/XXPS2UOWSWD2Y.ZJAAA
+        pub fn created(&self) -> DateTime<Utc> {
-        let pieces = gather_pieces(&req)?;
+            todo!()
-        let signing_string = make_signing_string(&pieces);
+        }
-        let signature = create(&signing_string, alg, private_key, key_id, pieces)?;
+        /// If specified, get the expiry time.
-        req.headers_mut().insert("signature", render(signature));
+        pub fn expires(&self) -> Option<DateTime<Utc>> {
-        Ok(())
+            todo!()
+        }
+        /// Retrieve the algorithm used for the signature.
+        pub fn algorithm(&self) -> Algorithm {
+            self.alg
+        }
+        /// Attempt to extract a signature from a request.
+        pub fn derive<T>(req: &Request<T>) -> Result<Signature<'_>, String> {
+            parse(req)
+        }
+        /// Attach `self` to `req` as the `signature` header.
+        pub fn attach_to<T>(self, req: &mut Request<T>) {
+            req.headers_mut().insert("signature", render(self));
+        }
     }
 
     /// Gather all the bits from a `Request`.
-    fn gather_pieces(req: &Request<Body>) -> Result<Vec<Component>, &'static str> {
+    fn gather_pieces<T>(req: &Request<T>) -> Result<Vec<Component>, &'static str> {
         let target = {
             let method = req.method().as_str().to_lowercase();
             let path = req.uri().path();
@@ -245,7 +450,7 @@ pub mod keys {
             ("host", req.uri().host().unwrap().to_owned()),
         ];
 
-        if [Method::POST, Method::PUT, Method::PATCH].contains(req.method()) {
+        if let Method::POST | Method::PUT | Method::PATCH = *req.method() {
             let digest = req
                 .headers()
                 .get("digest")
@@ -269,28 +474,29 @@ pub mod keys {
 
     /// Sign the `signing_string`.
     fn create<'s>(
-        signing_string: &'s str,
+        signing_string: String,
         alg: Algorithm,
-        key_pem: &str,
+        key: &Private,
         key_url: &'s str,
         components: Vec<Component>,
     ) -> Result<Signature<'s>, String> {
         let created = components
             .iter()
-            .find_map(|(k, v)| if *k == "(created)" { Some(v) } else { None })
+            .find_map(|(k, v)| (*k == "(created)").then_some(v))
             .cloned()
             .unwrap();
         let expires = components
             .iter()
-            .find_map(|(k, v)| if *k == "(expires)" { Some(v) } else { None })
+            .find_map(|(k, v)| (*k == "(expires)").then_some(v))
             .cloned()
             .unwrap();
-        // We regardless of the algorithm, we produce RSA-SHA256 signatures, because this is broadly compatible
+        // Regardless of the algorithm, we produce RSA-SHA256 signatures, because this is broadly compatible
         // with everything.
-        let signature = sign_rsa_sha256(signing_string, key_pem)?;
+        let signature = sign_rsa_sha256(&signing_string, key)?;
-        let encoded = base64(signature);
+        let encoded = BASE64_STANDARD.encode(signature);
         Ok(Signature {
             signature_encoded: encoded,
+            signing_string: signing_string.into(),
             key_id: key_url,
             components,
             created,
@@ -300,23 +506,13 @@ pub mod keys {
     }
 
     /// `rsa-sha256` is created using an rsa key and a sha256 hash.
-    fn sign_rsa_sha256(signing_string: &str, key_pem: &str) -> Result<Vec<u8>, String> {
+    fn sign_rsa_sha256(signing_string: &str, key: &Private) -> Result<Vec<u8>, String> {
-        use rsa::{
+        let Private(rsa) = key.clone();
-            signature::{Signer as _, SignatureEncoding as _},
-            RsaPrivateKey,
-        };
-        let rsa = RsaPrivateKey::from_pkcs8_pem(key_pem).map_err(|e| e.to_string())?;
         let key = SigningKey::<sha2::Sha256>::new(rsa);
         let buf = key.sign(signing_string.as_bytes()).to_vec();
         Ok(buf)
     }
 
-    fn base64(buf: Vec<u8>) -> String {
-        use base64::Engine as _;
-        // STANDARD works on masto, url safe does not.
-        base64::prelude::BASE64_STANDARD.encode(buf)
-    }
-
     /// Format the signature.
     fn render(sig: Signature<'_>) -> HeaderValue {
         let headers = sig
@@ -353,4 +549,71 @@ pub mod keys {
             .try_into()
             .expect("signature formatting should give a correct header value")
     }
+
+    // TODO: clean this mess up
+    fn parse<'s, T>(req: &'s Request<T>) -> Result<Signature<'s>, String> {
+        let Some(sig_header) = req.headers().get("signature").and_then(|v| v.to_str().ok()) else {
+            do yeet "No signature header";
+        };
+
+        let stuff: HashMap<&str, &str> = sig_header
+            .split(", ")
+            .filter_map(|piece| piece.split_once('='))
+            // TODO: technically more liberal than the spec
+            .map(|(k, v)| (k, v.trim_matches('"')))
+            .collect();
+
+        let inputs: Vec<&str> = stuff["headers"].split(' ').collect();
+
+        let (created, expires) = if inputs.contains(&"(created)") && inputs.contains(&"(expires)") {
+            (stuff["created"].to_string(), stuff["expires"].to_string())
+        } else {
+            // TODO: support "date" header instead of created/expires
+            do yeet "Only (created) + (expires) is currently supported";
+        };
+
+        let alg = match stuff.get("algorithm") {
+            Some(&"hs2019") => HS2019,
+            Some(&"rsa-sha256") => RSA_SHA256,
+            Some(alg) => do yeet format!("unsupported alg: {alg}"),
+            None => do yeet "Missing `algorithm`",
+        };
+
+        let components = {
+            let target = {
+                let method = req.method().as_str().to_lowercase();
+                let path = req.uri().path();
+                format!("{method} {path}")
+            };
+
+            let Some(host) = req.headers().get("host").and_then(|v| v.to_str().ok()) else {
+                do yeet "host header is required"
+            };
+            let mut components = vec![
+                ("(request-target)", target),
+                ("(created)", created.clone()),
+                ("(expires)", expires.clone()),
+                ("host", req.uri().host().unwrap_or(host).to_owned()),
+            ];
+
+            if let Method::POST | Method::PUT | Method::PATCH = *req.method() {
+                let Some(digest) = req.headers().get("digest").and_then(|v| v.to_str().ok()) else {
+                    do yeet "Digest header is required for POST/PATCH/PUT"
+                };
+                components.push(("digest", digest.to_string()));
+            }
+            components
+        };
+        let signing_string = make_signing_string(&components).into();
+
+        Ok(Signature {
+            key_id: stuff["keyId"],
+            signature_encoded: stuff["signature"].to_string(),
+            alg,
+            created,
+            expires,
+            components,
+            signing_string,
+        })
+    }
 }

lib/puppy/Cargo.toml

@@ -12,3 +12,4 @@ bincode = "2.0.0-rc.3"
 chrono = "*"
 either = "*"
 derive_more = "*"
+serde_json = "*"

lib/puppy/src/context.rs

@@ -2,7 +2,7 @@ use std::sync::OnceLock;
 
 use store::{Key, Store, Transaction};
 
-use crate::{config::Config, data::schema, Error, Result};
+use crate::{auth, config::Config, data::schema, Error, Result};
 
 /// The context of a running ActivityPuppy.
 ///
@@ -29,6 +29,10 @@ impl Context<'_> {
     pub fn mk_url(&self, key: Key) -> String {
         format!("https://{}/o/{key}", self.config.ap_domain)
     }
+    /// Get the verification actor.
+    pub fn verifier(&self) -> &auth::Verifier {
+        todo!()
+    }
 }
 
 /// The store, which we initialize only once this way.
@@ -48,6 +52,7 @@ where
     let cfg = Config {
         ap_domain: String::from("test.piss-on.me"),
         wf_domain: String::from("test.piss-on.me"),
+        port: 1312,
     };
     let db = STORE
         .get_or_try_init(|| Store::open(".state", schema()))

lib/puppy/src/lib.rs

@@ -1,3 +1,6 @@
+//! If you're an ActivityPub developer looking for information about ActivityPuppy's federation behavior,
+//! you should take a look at [`fetch`].
+
 // Working with result types is such a bitch without these.
 #![feature(iterator_try_collect, try_blocks, once_cell_try)]
 // Cause an error if someone tries to call [`context`] from within this crate. If we need one,
@@ -49,10 +52,10 @@ pub fn get_local_ap_object(cx: &Context<'_>, key: Key) -> Result<fetch::Object>
                 inbox: inbox.into(),
                 account_name: account_name.0,
                 display_name,
-                public_key: fetch::PublicKey {
+                public_key: fetch::Key {
                     owner: obj.id.0.into(),
                     key_id: key_id.into(),
-                    public_key_pem: key_pem,
+                    inner: key_pem,
                 },
             }))
         }
@@ -84,6 +87,7 @@ pub fn get_local_ap_object(cx: &Context<'_>, key: Key) -> Result<fetch::Object>
 }
 
 pub mod actor {
+    use fetch::signatures::Private;
     use store::{Key, StoreError, Transaction};
 
     use crate::{
@@ -161,14 +165,12 @@ pub mod actor {
         domain: &str,
     ) -> Result<(), StoreError> {
         let key_id = format!("https://{domain}/o/{vertex}#sig-key");
-        let (private, public) = fetch::keys::gen_keypair();
+        let (private, public) = Private::gen();
         tx.add_mixin(vertex, PublicKey {
-            key_pem: public.to_pem(),
+            key_pem: public.encode_pem(),
             key_id,
         })?;
-        tx.add_mixin(vertex, PrivateKey {
+        tx.add_mixin(vertex, PrivateKey { key_pem: private.encode_pem() })?;
-            key_pem: dbg!(private.to_pem()),
-        })?;
         store::OK
     }
 }
@@ -189,8 +191,129 @@ pub enum Error {
 }
 
 pub mod config {
+    #[derive(Clone)]
     pub struct Config {
         pub ap_domain: String,
         pub wf_domain: String,
+        pub port: u16,
+    }
+}
+
+pub mod auth {
+    use fetch::signatures::{Private, Public, Signature};
+    use serde_json::{json, Value};
+
+    use crate::config::Config;
+
+    pub struct Verifier {
+        actor_id: String,
+        key_id: String,
+        private: Private,
+        public: Public,
+    }
+
+    impl Verifier {
+        pub async fn get_public_key(&self, uri: &str) -> Result<fetch::Key, String> {
+            let json = fetch::resolve(&self.signing_key(), uri).await.unwrap();
+            // TODO: make this parsing work better.
+            Ok(fetch::Key {
+                key_id: json["publicKey"]["id"].as_str().unwrap().to_string().into(),
+                owner: json["publicKey"]["owner"]
+                    .as_str()
+                    .unwrap()
+                    .to_string()
+                    .into(),
+                inner: json["publicKey"]["publicKeyPem"]
+                    .as_str()
+                    .unwrap()
+                    .to_string()
+                    .into(),
+            })
+        }
+
+        pub fn signing_key(&self) -> fetch::SigningKey {
+            fetch::Key {
+                key_id: self.key_id.clone(),
+                owner: self.actor_id.clone(),
+                inner: self.private.clone(),
+            }
+        }
+
+        pub fn to_json_ld(&self) -> Value {
+            json!({
+                "@context": [
+                    "https://www.w3.org/ns/activitystreams",
+                    "https://w3id.org/security/v1",
+                ],
+                "id": self.actor_id,
+                "name": "Public key fetcher",
+                "publicKey": {
+                    "id": self.key_id,
+                    "owner": self.actor_id,
+                    "publicKeyPem": self.public.encode_pem()
+                },
+                "type": "Service",
+            })
+        }
+
+        pub fn load(cfg: &Config) -> Verifier {
+            let domain = &cfg.ap_domain;
+            let private = Private::load(".state/fetcher.pem");
+            Verifier {
+                actor_id: format!("https://{domain}/s/request-verifier"),
+                key_id: format!("https://{domain}/s/request-verifier#sig-key"),
+                public: private.get_public(),
+                private,
+            }
+        }
+    }
+
+    /// An ActivityPub actor that signed a request.
+    pub struct Signer {
+        /// The ActivityPub ID (a URL) of the signer of the request.
+        pub ap_id: String,
+    }
+
+    pub enum SigError {
+        FailedToFetchKey { keyid: String },
+        ParseSignature { error: String },
+        VerificationFailed { error: String },
+    }
+
+    /// Check the signature for a request.
+    pub async fn verify_signature(
+        req: &fetch::http::Request<impl AsRef<[u8]>>,
+        cfg: &Config,
+    ) -> Result<Option<Signer>, SigError> {
+        if req.uri().path() == "/s/request-verifier" {
+            // Allow access to the request verifier actor without checking the signature.
+            return Ok(None);
+        }
+        if req.headers().get("signature").is_none() {
+            // Request is not signed!
+            return Ok(None);
+        };
+
+        // Parse the signature.
+        let sig = match Signature::derive(&req) {
+            Ok(signature) => signature,
+            Err(error) => return Err(SigError::ParseSignature { error }),
+        };
+
+        // Fetch the public key using the verifier private key.
+        let verifier = Verifier::load(cfg);
+        let Ok(public_key) = verifier.get_public_key(sig.key_id()).await else {
+            return Err(SigError::FailedToFetchKey {
+                keyid: sig.key_id().to_string(),
+            });
+        };
+
+        // Verify the signature header on the request.
+        let public_key = public_key.upgrade();
+        if let Err(error) = public_key.verify(sig) {
+            Err(SigError::VerificationFailed { error })
+        } else {
+            Ok(Some(Signer { ap_id: public_key.owner.into() }))
+        }
     }
 }

lib/puppy/src/post.rs

@@ -4,6 +4,7 @@ use std::ops::RangeBounds;
 
 use chrono::{DateTime, Utc};
 use either::Either::{Left, Right};
+use fetch::signatures::Private;
 use store::{util::IterExt as _, Key, Store, StoreError, Transaction};
 
 use crate::{
@@ -33,9 +34,14 @@ impl Post {
             id: post.id().clone().into(),
             object: Box::new(post),
             kind: String::from("Create"),
-            actor: author_id.0.into(),
+            actor: author_id.0.clone().into(),
         };
         let (private, public) = cx.db.get_mixin_many::<(PrivateKey, PublicKey)>(author)?;
+        let key = fetch::SigningKey {
+            key_id: public.key_id,
+            owner: author_id.0,
+            inner: Private::decode_pem(&private.key_pem),
+        };
         // Insert the activity in the database.
         cx.run(|tx| try {
             let activity_key = Key::gen();
@@ -53,13 +59,7 @@ impl Post {
             tx.add_alias(activity_key, id)?;
         })?;
         // Send the requests.
-        fetch::deliver(
+        fetch::deliver(&key, activity, "https://crimew.gay/users/ezri/inbox").await;
-            &private.key_pem,
-            &public.key_id,
-            activity,
-            "https://crimew.gay/users/ezri/inbox",
-        )
-        .await;
         Ok(())
     }
 }