If you think of an authentication method, the first method that will come to your mind will always be the combination of a username and a password. While its simplicity makes it one of the most extended authentication methods in all kinds of software, it is not the safest method. The multifactor authentication approach combines a set of authentication methods. Access is granted only if each method derives a positive result. Two-factor authentication and three-factor authentication involve two and three authentication factors, respectively. Although two-factor authentication and above are often considered to be strong authentication methods and are in fact more secure, you can also achieve strong authentication for your service using only one authentication factor. There are three kinds of authentication factors that serve as a taxonomy for authentication techniques: the knowledge factor, the possession factor, and the inherence factor.