Add signer-proxy as a recommended solution for AWS KMS or YubiHSM key management

Author: upnodedev

pages/builders/chain-operators/management/key-management.mdx

@@ -26,6 +26,10 @@ Key Management Systems (KMS) that can work with your developer operations
 configurations. This can be used in conjunction with the `eth_signTransaction`
 RPC method.
 
+If you intend to manage your keys using AWS KMS or YubiHSM2, you can use [signer-proxy](https://github.com/upnodedev/signer-proxy).
+
+[signer-proxy](https://github.com/upnodedev/signer-proxy) is an open-source tool that connects to your AWS KMS or YubiHSM2 backend and exposes an endpoint compatible with the `eth_signTransaction` RPC method.
+
 <Callout type="info">
   You can take a look at the signer client [source code](https://github.com/ethereum-optimism/optimism/blob/develop/op-service/signer/client.go)
   if you're interested in what's happening under the hood.