User authentication is the process of confirming that a person attempting to access a system, application, or online service is who they claim to be. It is a fundamental component of cybersecurity and digital identity management, helping organizations protect sensitive data, prevent unauthorized access, and reduce the risk of fraud. Authentication methods include passwords, one-time passwords (OTPs), biometric verification such as fingerprint or facial recognition, security tokens, passkeys, and multi-factor authentication (MFA). Many organizations also use risk-based authentication, device fingerprinting, and behavioral analytics to assess login attempts and detect suspicious activity.