Which user authentication method is known for its scalability?

LDAP (Lightweight Directory Access Protocol) is recognized for its scalability in user authentication. This method is designed to work efficiently within large environments, enabling organizations to maintain and manage a centralized directory service that can accommodate a vast number of users without significant performance degradation.

LDAP is commonly used in enterprise environments where there is a need to enforce consistent authentication policies across multiple applications and services. Its architecture allows it to efficiently handle a large volume of queries and updates, essential for organizations that require a responsive and reliable authentication service as they scale.

In contrast, methods such as local users or a local database typically manage authentication on a smaller scale. These approaches can become cumbersome and less efficient when applied to a larger number of users, as they lack the centralized management capabilities that LDAP provides. RADIUS, while also scalable and widely used for network access control, is often more complex to implement and manage in comparison to LDAP's straightforward directory structure.