Google Oauth IdToken to backend

[Pdev]

Hello, 

I was wondering if there was any way to forward the Google Id Token to the backend when using a Google Oauth2.0 Server.
Right now, the fortiweb puts in "authorization" header "Bearer + Google AccessToken"

But I would like this header to contain "Bearer + Google IdToken"

The difference for me is that Google IdToken is a Jwt that can be decoded and verified easily in my backend and so can be used as is to authenticate everything in my backend.

On the other hand the AccessToken is opaque and only give me access to GoogleApis. So this means I would need to mint my own Jwt with the infos I get from /userinfos google endpoint.

Thanks in advance, 

Jules