Add Google login and registration to WordPress
1) Create a Google Sign-in project
Navigate to https://developers.google.com/identity/sign-in/web/sign-in and click the "Configure a project" button. A new window will open which will guide you through the setup of a new project. From the dropdown then click "Create a new project" and type the name of the project.
After clicking next, you'll be presented with the above screen. Simply type anything in there and then click next.
2) Configure your project
3) Add credentials to WordPress
After clicking create you'll be given your credentials that you need to add into your WordPress website. Do not click on "Done" yet.
After you've got your credentials. Login into your WordPress dashboard and navigate to "Users -> Settings -> General -> Social Login" and locate the settings "Google Client ID" and "Google Client Secret" and type in the credentials given to you by Google and save the settings.
4) Last steps
From the previous popup, click on the "API Console" link at the bottom of the popup, in the new page, click the "Enable apis and services" button.
Search for "identity" and then click on "Identity toolkit API" and then click on "Enable".
After a few seconds, the API will be enabled and you'll be redirected to a dashboard for your app. From this screen there's one last thing you need to do. Click on "Credentials" in the right side of the screen then select "Oauth client" and you should see a page like this:
Your Google Sign in is now ready to be used :)