Did you manage to solve this?
Edit: for now a workarround seems to have a page just for signin/signup, and to register its url in the google api console.
In this page, you can set a workflow that when the page is loaded, signup/login the user with google.
Then, if you want to login from a popup, you add a link element that open this page in a new tab.
The only thing I am missing is to find a way to close this tab once the user is logged in.
Is there any way to close an opened tab?
Edit 2: to close the opened tab once the user is logged in, just add an html element with a custom state “content” as text. Then in the html element, set the content to
Finally in the workflow, run a workflow when the user is logged in that change the html content to “window.close();”
Now I am able to login/signup to Google+ from any page of my website and without leaving it 