Whilst the growing number of identity management systems have the potential to reduce the threat of identity attacks, major deployment problems remain because of the lack of interoperability between such systems. In this paper we propose a simple scheme to provide client-based interoperation between OAuth and an Information Card-based system such as CardSpace or Higgins. In this scheme, Information Card users are able to obtain an assertion token from an OAuth-enabled system, the contents of which can be processed by an Information Card-enabled relying party. The scheme, based on a browser extension, is transparent to OAuth providers and to identity selectors, and only requires minor changes to the operation of an Information Card-enabled relying party. We specify its operation and also describe an implementation of a proof-of-concept prototype. Additionally, security and operational analyses are provided.