This module will allow you to add Time-based One-time Password Algorithm (also called "Two Step Authentication" or "Multi-Factor Authentication") support to user logins. It works with Google's Authenticator app system and support most (if not all) OATH based HOTP/TOTP systems.

Drupal 8

There is a release out that is integrated with the TFA module. More documentation will be coming.

Drupal 7 Remark

If you want to protect uid 1, you have to enable the option 'Protect my account with two-factor-authentication' on user/1/edit!

Drupal 7 Dependencies

Drupal 7 Recommended Modules

This module now supports both QR Codes and Mobile Codes, although we recommend using Mobile Codes, because it has more flexibility (there is a default preset for Mobile Codes which can be altered to your need: different providers and adjustable options per provider)

Supporting organizations: 

Project information