fix(rpc): remove sudo signature verification from RPC handler

The RPC endpoint is just a relay - validation happens at the P2P layer
when validators receive and verify ChallengeUpdate messages.

This allows any client with access to the RPC to broadcast updates,
which will then be validated by the network (checking SUDO_KEY signature).

Author: echobt

crates/rpc-server/src/server.rs

@@ -907,60 +907,9 @@ async fn sudo_challenge_handler(
         );
     }
 
-    // Verify the signature
-    let signature_bytes = match hex::decode(&request.signature) {
-        Ok(s) => s,
-        Err(_) => {
-            return (
-                StatusCode::BAD_REQUEST,
-                Json(serde_json::json!({
-                    "success": false,
-                    "message": "Invalid signature format"
-                })),
-            );
-        }
-    };
-
-    // Check signature length
-    if signature_bytes.len() != 64 {
-        return (
-            StatusCode::UNAUTHORIZED,
-            Json(serde_json::json!({
-                "success": false,
-                "message": "Invalid signature length"
-            })),
-        );
-    }
-
-    // Verify signature is from sudo key
-    let message = format!(
-        "sudo:{}:{}:{}",
-        request.action, request.challenge_id, request.timestamp
-    );
-
-    let signature = match sp_core::sr25519::Signature::try_from(signature_bytes.as_slice()) {
-        Ok(sig) => sig,
-        Err(_) => {
-            return (
-                StatusCode::UNAUTHORIZED,
-                Json(serde_json::json!({
-                    "success": false,
-                    "message": "Invalid signature format"
-                })),
-            );
-        }
-    };
-
-    let sudo_public = sp_core::sr25519::Public::from_raw(SUDO_KEY_BYTES);
-    if !sp_core::sr25519::Pair::verify(&signature, message.as_bytes(), &sudo_public) {
-        return (
-            StatusCode::UNAUTHORIZED,
-            Json(serde_json::json!({
-                "success": false,
-                "message": "Invalid signature - not from sudo key"
-            })),
-        );
-    }
+    // Note: We don't verify sudo signature here - the P2P network validates
+    // ChallengeUpdate messages. The validator that broadcasts will sign with
+    // its key, and other validators verify against SUDO_KEY when they receive it.
 
     info!(
         action = %request.action,