NOTE: Only Workspaces on the Business and Enterprise plans can enable mandatory Google sign-in for Circle members.
NOTE: Only Admins and Billing Moderators with unique domains can enable this feature. Domains like gmail.com, hotmail.com cannot use this feature.
Go to your Workspace's Settings page.
Then, click Security.
Click the toggle to turn Google sign-in on/off.
Select Enable.
When enabled, your team members must use Google sign-in to access the Workspace.