You can set up two-factor authentication for the users in your directory. Two-factor authentication (or 2FA) provides an extra layer of account security during sign-in by requiring not only the password, but also a code from an authentication app sent to the user’s device. 

By default, 2FA is switched off for newly created directories. You can turn it on using the following steps. 

Steps: 

1. In your directory, click the Security tab. 
2. From the left menu, select Two-factor authentication. 
3. In the Two-factor authentication panel, turn on the Two-factor authentication switch.  
4. In the App display name field, enter the name that your users will see in their authentication app. 
5. Optional: If you want to make 2FA mandatory for all users, select the Enforce for all users checkbox. 
6. Click Save.