Cloud Kicks (CK) has built a site using Salesforce Experience Builder.

Set up a login flow for communities that accepts the customers' Google credentials and matches with the credentials stored on the user records in Salesforce.

Create a custom self-registration page and a custom login page by using Visualforce and Apex controllers.

Create an Authentication Provider by choosing Google as the provider type and add relevant parameters to access the customers' basic profile data.

Create a custom login page using Lightning components and use the Google REST API to access customers' basic profile data.