User authentication in web applications is crucial for ensuring that only authorized users can access specific resources and functionalities. It involves verifying a user's identity, typically through methods like passwords, biometrics, or 2-factor authentication. Effective authentication enhances security, reduces the risk of data breaches, and builds user trust. Moreover, it plays a significant role in securing sensitive information, maintaining privacy, and complying with regulations in various applications, particularly those involving financial transactions or personal data.