Duo Security - Business is Basic two-factor authentication for your entire team, Secure on-premises apps, All authentication methods User self-enrollment
Two-factor authentication provides a second layer of security to any type of login, requiring extra information or a physical device to log in, in addition to your password.
The factors may include:
Something you know a unique username and password
Something you have a smartphone with an app to approve authentication requests
Something you are biometrics - like your fingerprint or a retina scan
By choosing two different channels of authentication, you can protect user logins from remote attacks that may exploit stolen credentials.
For example, your first factor may be your password, while your second factor is sent via a push notification generated by an authentication mobile app on your smartphone that you must approve.