From 1473e726f3d4a3dfba2f07134d4237ebc8e2c1b2 Mon Sep 17 00:00:00 2001
From: Claude <claude@example.com>
Date: Thu, 13 Aug 2026 02:10:09 +0000
Subject: [PATCH] webhook: compare secret in constant time

payload.secret != expected_secret short-circuits on the first
differing byte, which leaks timing information about how many
leading bytes of a guess are correct. Use subtle::ConstantTimeEq
instead.
---
 Cargo.toml     | 1 +
 src/webhook.rs | 5 ++++-
 2 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/Cargo.toml b/Cargo.toml
index 2bc0ec5..f5459ae 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -18,6 +18,7 @@ reqwest = {
 serde = { version = "1", features = ["derive"] }
 serde_json = "1"
 sha2 = "0.10"
+subtle = "2"
 sqlx = {
   version = "0.8",
   features = [
diff --git a/src/webhook.rs b/src/webhook.rs
index 2223c17..fab543e 100644
--- a/src/webhook.rs
+++ b/src/webhook.rs
@@ -1,5 +1,6 @@
 use axum::{extract::State, http::StatusCode, response::IntoResponse};
 use serde::Deserialize;
+use subtle::ConstantTimeEq;
 
 use crate::AppState;
 
@@ -28,7 +29,9 @@ pub async fn receive(
             .into_response();
     };
 
-    if payload.secret != expected_secret {
+    let secret_matches = payload.secret.as_bytes().ct_eq(expected_secret.as_bytes());
+
+    if !bool::from(secret_matches) {
         tracing::warn!("received webhook with invalid secret");
 
         return (StatusCode::UNAUTHORIZED, "invalid webhook secret").into_response();