Authenticating Google users without registering application first

Question

The old Google OpenID endpoint provided a way of authenticating users without having to register your application first. This was very convenient for open source applications because they could provide a "log in with Google" option which would work out of the box. For instance, Google's own code review tool Gerrit makes use of this.

It appears that this endpoint is deprecated and will be shutdown: https://developers.google.com/accounts/docs/OpenID2

My question is twofold:

1. Is the endpoint that's going to be shutdown the one at https://www.google.com/accounts/o8/id used by StackOverflow, Gerrit etc.? (With all the different OAuth and OpenID variants mentioned in Google's docs, it's not terribly clear.)

2. If so, is there any non-deprecated login option that doesn't require the application to be registered.

Answer 1

Indeed OpenID2 is deprecated, and that is the endpoint at https://www.google.com/accounts/o8/id;

Open-Source code can still be written; it will require just that the site integrating the open-source solution perform the registration step and supply the registration values (client_id, redirect_uri) to the open-source code. If you write the code with a modular approach to configuring the registration data, the code can be highly re-usable.