In the modern age, web applications have become a critical part of everyone’s life; every second they grant access to the digital world to hundreds of millions of people. This relevance required the implementation of authentication mechanisms that could help us identify the user, both for efficiency and security. One of the most employed strategies in this field nowadays is the use of 2-Factor Authentication (2FA) and, in particular, the adoption of One-Time Passwords (OTPs). Authentication mechanisms, however, have to be thoroughly developed because they are one of the most interesting – and thus – attacked points on the surface of an application.