Google Authenticator provides one-time passwords to smartphone owners for multifactor authentication, or you can integrate it into other applications, such as blogs.
Login security increases significantly when using a combination of factors to authenticate a user (i.e., multifactor authentication). In most situations, two-factor authentication is usually enough. The first authentication factor is usually a password or key, with various possibilities for the second factor, including hardware tokens owned by authorized users or one-time password (OTP) generators that provide OTP tokens. One-time passwords come in several varieties (e.g., hardware, software, grid card). A popular, free, and simple way to implement two-factor authentication (2FA) with OTP is Google Authenticator, which is available in the form of an app for iOS and Android and as source code  for the server side.
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