Put more simply, you can redefine the handleAuth function to automatically set the allow property to true
window.handleAuth=function(a){ a.allow = true; a.logoutUrl?window.location.href=a.redirectUrl:window.location.reload()}
and then click the button.
But it won't help for the reasons explained above.
Which opens https://foobar.withgoogle.com/login
There, an object a:
a = {
Is passed to the original window's handleAuth function:window.handleAuth=function(a){ a.logoutUrl?window.location.href=a.redirectUrl:window.location.reload()}
It seems that the allow property of the object passed is never checked :(