This document describes, among other things, security hardening techniques that guard against certain client-side attack vectors. These techniques generally involve the use of an intermediary that detects and handles identity service transactions on behalf of a client. In one embodiment, the intermediary establishes a resource domain session with the client in order to provide the client with desired resource domain content or services from a resource domain host. The intermediary detects when the resource domain host invokes a federated identity service as a condition of client access. The intermediary handles the identity transaction in the identity domain on behalf of the client within the client's resource domain session. Upon successful authentication and/or authorization with an IdP, the intermediary connects the results of the identity services domain transaction to the resource domain.