Disabling unauthenticated sign-ups
If you're using built-in authentication, you can block unauthenticated people from being able to create an account.
- 
In the upper-right corner of any page, click .  
- 
In the left sidebar, click Management Console.  
- 
In the left sidebar, click Privacy.  
- 
Unselect Enable sign-up.  
- 
Under the left sidebar, click Save settings. 