Sample code to access cloud.google.com / google compute engine ?

Does anyone happen to have some boilerplate code which they can share
that uses Pike to get the authorisation tokens required to create
and delete google compute engine instances?

Basically I need to follow this guide:

https://developers.google.com/identity/protocols/OAuth2ServiceAccount

Which means that I have a private service key from google, and need to
use this to create a JWT, which can then be used to request a token.
The token I can then use to call the API.

The question is, how do I use Web.Auth to get my hands on the token?
The example shown in http://pike.lysator.liu.se/generated/manual/modref/ex/predef_3A_3A/Web/Auth.html
appears to be geared towards authorisations that require user approval.

In my case I only need to call some Google API (server to server), no userdata
involved.
-- 
Stephen.