Cross Client Auth in Javascript

[Hank Zill]

I'm trying to get the Cross Client authentication stuff working with the Javascript API. I'm trying to adapt the documentation available at https://developers.google.com/identity/protocols/CrossClientAuth to the Javascript API, passing the magic  'audience:server:client_id:[MY_SERVER_CLIENT_ID]' as a scope in both the gapi.auth2.init() and in grantOfflineAccess(). However, this just results in an 'invalid_scope' error from Google.

Has anyone managed to get Cross Client stuff working with Javascript? How did you do it? I have it working between my server and an iOS app, but I need to also add a Javascript client to the mix.

Thanks!