Authentication (AuthN) is the process of verifying the identity of users or systems before granting access to resources. This blog explores various AuthN methods like passwords, multi-factor authentication, and biometrics, and discusses the trade-offs of building in-house or using third-party providers. Authentication ensures security in applications by determining who (or what) is attempting to access a system. Different authentication methods include username and password, Multi-Factor Authentication (MFA), Single Sign-On (SSO) with an Identity Provider (IdP), Biometrics, QR codes, Magic links and One-Time Passcodes (OTP), and Tokens. Prioritizing passwordless authentication, implementing account lockout policies, and secure session management are some best practices for AuthN. It is recommended to use well-supported libraries and frameworks or managed authentication services provided by platforms like WorkOS instead of building your own authentication system.