two factor authentication (TFA) implementation
A great pattern that we are seeing for implementing two-factor authentication is to use the TOTP (Time-based One-time Password Algorithm) standard for the second authentication step. What is so cool about TOTP is that it is flexible enough to allow your users to generate their authentication tokens directly on their smart phones using a TOTP app like Google Authenticator or have their tokens sent to their mobile phone via SMS.
Twillio - send SMS cell phone message, voice message and Authentication API for every application
GAuthify -Google® Authenticator, SMS, Voice, and Email Two-Factor Authentication in 5 minutes.