Barebones two-factor authentication with Devise

Devise-Two-Factor is a minimalist extension to Devise which offers support for two-factor authentication, through the TOTP scheme. It:Allows you to incorporate two-factor authentication into your existing modelsIs opinionated about security, so you don't have to beIntegrates easily with two-factor applications like Google Authenticator and AuthyIs extensible, and includes two-factor backup codes as an example of how plugins can be structured.