I tried to implement this where I inserted my google client id key and my gmail password, at the fields key and password located at:
saleor dashboard > configuration > site settings > authorization key > google auth2.0.
Output I get is:
error400
redirect uri mismatch
Apart from adding authorization key in Saleor's dashboard, you should enter the Google API Console and add the
http://yourwebsite.com/complete/google-oauth2/
URL in there. Please make sure that's the exact URL your site is redirecting to, as simple changes: eg protocol, or trailing slash will make it not work.