User management is the process of identifying, authorizing, and authenticating users to provide secure access to digital resources, with authentication serving as a critical component in confirming user identities without revealing passwords. It involves various aspects, including user profiles, properties, privileges, and migration, and can be enhanced through the use of APIs for managing user identities and access from a central location, improving efficiency, security, and user experience. Authentication methods range from single-factor, such as passwords, to more secure options like two-factor and biometric authentication, with the choice depending on balancing user experience and system security. The text contrasts traditional user management, which is prone to vulnerabilities and inefficiencies, with real-time approaches that enhance security by validating credentials instantly. Authentication services complement user management by enforcing strong password policies, managing access across devices, and implementing multi-factor authentication to reduce unauthorized access risks. Effective user management systems, such as those offered by providers like Clerk, are crucial for startups and small-to-medium businesses to handle user identities efficiently while ensuring compliance with security policies.