Google Contact Sync requires you to use Google OAuth and generate a client ID and client secret for your install.
First, go to https://console.developers.google.com/apis/credentials and then click create credentials.
If you haven’t done so already, Google will prompt you to create a OAuth consent screen. Google requires this, so follow their on-screen instructions to do that.
Once you have a OAuth consent screen, click Credentials in the left menu, followed by + Create Credentials at the top of the page.
Choose OAuth client ID. When setting up your project, choose Web Application and add your domain.
Next you need to enter a redirect URL as below
Being sure to replace https://yoursite.com/ with your site information.
You’ll also need to setup the oAuth consent screen. This is what you are redirected to when clicking to authenticate Google.
Finally, the domain verification so that you only give access via an approved domain.
Once all this is set up, you’ll be given your client ID and client secret.