What is Two-Step (Multi-factor) Authentication?
Two step authentication - also known as multi-factor authentication (MFA) - is a method of confirming a user's claimed identity in which a computer user is granted access only after successfully presenting two or more pieces of evidence (or factors) to an authentication mechanism: knowledge (something the user and only the user knows), possession (something the user and only the user has), and inherence (something the user and only the user is).
Some common forms of second factors are one-time passcode (OTP) sent through SMS, voice call or from mobile app.
MFA has been widely used in online banking as one example.