From 89f5b200a8128180504716cb829b9270a61dbe8b Mon Sep 17 00:00:00 2001
From: alemi <me@alemi.dev>
Date: Sun, 23 Jun 2024 03:55:03 +0200
Subject: [PATCH] feat: added hmac validated proxy route

---
 Cargo.lock                                 |  3 +++
 upub/core/src/config.rs                    |  3 +++
 upub/routes/Cargo.toml                     |  5 +++-
 upub/routes/src/activitypub/application.rs | 29 +++++++++++++++++++++-
 upub/routes/src/activitypub/mod.rs         |  1 +
 5 files changed, 39 insertions(+), 2 deletions(-)

diff --git a/Cargo.lock b/Cargo.lock
index 0a2326e2..600c36dd 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -4864,7 +4864,9 @@ version = "0.2.0"
 dependencies = [
  "apb",
  "axum",
+ "base64 0.22.1",
  "chrono",
+ "hmac",
  "httpsign",
  "jrd",
  "mastodon-async-entities",
@@ -4874,6 +4876,7 @@ dependencies = [
  "sea-orm",
  "serde",
  "serde_json",
+ "sha2",
  "sha256",
  "thiserror",
  "time",
diff --git a/upub/core/src/config.rs b/upub/core/src/config.rs
index 49dbb6bb..640c49e8 100644
--- a/upub/core/src/config.rs
+++ b/upub/core/src/config.rs
@@ -68,6 +68,9 @@ pub struct SecurityConfig {
 	#[serde(default)]
 	pub allow_public_debugger: bool,
 
+	#[serde_inline_default("changeme".to_string())]
+	pub proxy_secret: String,
+
 	#[serde_inline_default(true)]
 	pub show_reply_ids: bool,
 
diff --git a/upub/routes/Cargo.toml b/upub/routes/Cargo.toml
index 978525fd..fc100481 100644
--- a/upub/routes/Cargo.toml
+++ b/upub/routes/Cargo.toml
@@ -13,7 +13,10 @@ readme = "README.md"
 [dependencies]
 thiserror = "1"
 rand = "0.8"
-sha256 = "1.5"
+sha2 = "0.10"
+sha256 = "1.5" # TODO ughhh
+hmac = "0.12"
+base64 = "0.22"
 chrono = { version = "0.4", features = ["serde"] }
 serde = { version = "1", features = ["derive"] }
 serde_json = "1"
diff --git a/upub/routes/src/activitypub/application.rs b/upub/routes/src/activitypub/application.rs
index 0c90a2af..115c193d 100644
--- a/upub/routes/src/activitypub/application.rs
+++ b/upub/routes/src/activitypub/application.rs
@@ -1,9 +1,11 @@
 use apb::{LD, ActorMut, BaseMut, ObjectMut, PublicKeyMut};
 use axum::{extract::{Path, Query, State}, http::HeaderMap, response::{IntoResponse, Redirect, Response}, Form};
+use hmac::{Hmac, Mac};
 use reqwest::Method;
+use base64::{engine::general_purpose::URL_SAFE, Engine as _};
 use upub::{traits::Fetcher, Context};
 
-use crate::{builders::JsonLD, AuthIdentity, Identity};
+use crate::{builders::JsonLD, ApiError, AuthIdentity, Identity};
 
 
 pub async fn view(
@@ -74,6 +76,31 @@ pub async fn proxy_form(
 	proxy(ctx, query, auth).await
 }
 
+pub async fn proxy_hmac(
+	State(ctx): State<Context>,
+	AuthIdentity(auth): AuthIdentity,
+	Path(hmac): Path<String>,
+	Path(uri): Path<String>,
+) -> crate::ApiResult<impl IntoResponse> {
+	let bytes = URL_SAFE.decode(hmac).map_err(|_| ApiError::bad_request())?;
+	let uri =
+		std::str::from_utf8(
+			&URL_SAFE.decode(uri).map_err(|_| ApiError::bad_request())?
+		)
+		.map_err(|_| ApiError::bad_request())?
+		.to_string();
+
+	type HmacSha256 = Hmac<sha2::Sha256>;
+	let mut mac = HmacSha256::new_from_slice(ctx.cfg().security.proxy_secret.as_bytes())
+		.map_err(|_| ApiError::internal_server_error())?;
+
+	mac.update(uri.as_bytes());
+	mac.verify_slice(&bytes)
+		.map_err(|_| ApiError::forbidden())?;
+
+	proxy(ctx, uri, auth).await
+}
+
 async fn proxy(ctx: Context, query: String, auth: Identity) -> crate::ApiResult<impl IntoResponse> {
 	// only local users can request fetches
 	if !ctx.cfg().security.allow_public_debugger && !auth.is_local() {
diff --git a/upub/routes/src/activitypub/mod.rs b/upub/routes/src/activitypub/mod.rs
index 61786da8..f04d3a2e 100644
--- a/upub/routes/src/activitypub/mod.rs
+++ b/upub/routes/src/activitypub/mod.rs
@@ -25,6 +25,7 @@ impl ActivityPubRouter for Router<upub::Context> {
 			.route("/proxy", post(ap::application::proxy_form))
 			.route("/proxy", get(ap::application::proxy_get))
 			.route("/proxy/:uri", get(ap::application::proxy_path))
+			.route("/proxy/:hmac/:uri", get(ap::application::proxy_hmac))
 			.route("/inbox", post(ap::inbox::post))
 			.route("/inbox", get(ap::inbox::get))
 			.route("/inbox/page", get(ap::inbox::page))