fix(iam): propagate cache miss load failures (#2692)

Co-authored-by: GatewayJ <8352692332qq.com>
Co-authored-by: loverustfs <hello@rustfs.com>
Co-authored-by: houseme <housemecn@gmail.com>

crates/iam/src/sys.rs

@@ -755,7 +755,7 @@ impl<T: Store> IamSys<T> {
                 Ok((Some(res), ok))
             }
             None => {
-                let _ = self.store.load_user(access_key).await;
+                self.store.load_user(access_key).await?;
 
                 if let Some(res) = self.store.get_user(access_key).await {
                     let ok = res.credentials.is_valid();
@@ -1372,6 +1372,10 @@ mod tests {
         }
 
         async fn load_user(&self, name: &str, user_type: UserType, m: &mut HashMap<String, UserIdentity>) -> Result<()> {
+            if user_type == UserType::Reg && name == "load-failure-user" {
+                return Err(Error::Io(std::io::Error::other("load user failed")));
+            }
+
             if user_type == UserType::Reg && name == "notify-user" {
                 let user = UserIdentity::from(Credentials {
                     access_key: name.to_string(),
@@ -1813,6 +1817,17 @@ mod tests {
         );
     }
 
+    #[tokio::test]
+    async fn test_check_key_propagates_cache_miss_load_failure() {
+        let store = StsTestMockStore { empty_policies: false };
+        let cache_manager = IamCache::new(store).await;
+        let iam_sys = IamSys::new(cache_manager);
+
+        let result = iam_sys.check_key("load-failure-user").await;
+
+        assert!(matches!(result, Err(Error::Io(_))));
+    }
+
     #[tokio::test]
     async fn test_prepare_auth_eval_matches_prepare_sts_auth_for_parent_policy_fallback() {
         let store = StsTestMockStore { empty_policies: false };